diff --git a/reclass_tools/cli.py b/reclass_tools/cli.py
index 2f1807d..898fd52 100644
--- a/reclass_tools/cli.py
+++ b/reclass_tools/cli.py
@@ -15,7 +15,6 @@
 from __future__ import print_function
 
 import argparse
-import os
 import sys
 import yaml
 
@@ -33,14 +32,22 @@
         command_method()
 
     def do_get_key(self):
-        results = walk_models.remove_reclass_parameter(
+        walk_models.remove_reclass_parameter(
             self.params.path,
             self.params.key_name,
             verbose=self.params.verbose,
             pretend=True)
 
+    def do_add_key(self):
+        walk_models.add_reclass_parameter(
+            self.params.path,
+            self.params.key_name,
+            self.params.add_value,
+            verbose=self.params.verbose,
+            merge=self.params.merge)
+
     def do_del_key(self):
-        results = walk_models.remove_reclass_parameter(
+        walk_models.remove_reclass_parameter(
             self.params.path,
             self.params.key_name,
             verbose=self.params.verbose,
@@ -62,7 +69,6 @@
         reclass_storage = reclass_models.reclass_storage(inventory=inventory)
         print('\n'.join(sorted(reclass_storage.keys())))
 
-
     def do_list_nodes(self):
         try:
             from reclass_tools import reclass_models
@@ -119,10 +125,15 @@
                                     action='store_const', const=True,
                                     help='Show verbosed output', default=False)
 
+        merge_parser = argparse.ArgumentParser(add_help=False)
+        merge_parser.add_argument('--merge', dest='verbose',
+                                  action='store_const', const=True,
+                                  help='Show verbosed output', default=False)
+
         key_parser = argparse.ArgumentParser(add_help=False)
         key_parser_help = (
-                'Key name to find in reclass model files, for example:'
-                ' parameters.linux.network.interface')
+            'Key name to find in reclass model files, for example:'
+            ' parameters.linux.network.interface')
         key_parser.add_argument('key_name', help=key_parser_help, default=None)
 
         keys_parser = argparse.ArgumentParser(add_help=False)
@@ -130,6 +141,12 @@
             'keys',
             help='Key names to find in reclass model files', nargs='*')
 
+        add_value_parser = argparse.ArgumentParser(add_help=False)
+        add_value_parser.add_argument(
+            'add_value',
+            help=('Value to add to the reclass model files, can be in the '
+                  'inline YAML format'))
+
         path_parser = argparse.ArgumentParser(add_help=False)
         path_parser.add_argument(
             'path',
@@ -175,8 +192,6 @@
             help=('YAML/JSON files with context data to render '
                   'the template'))
 
-
-
         parser = argparse.ArgumentParser(
             description="Manage virtual environments. "
                         "For additional help, use with -h/--help option")
@@ -184,13 +199,19 @@
                                            help='available commands',
                                            dest='command')
 
-        # TODO: add-class NNN [to] MMM.yml # can be used with 'render'
         subparsers.add_parser('get-key',
                               parents=[key_parser, path_parser,
                                        verbose_parser],
                               help="Find a key in YAMLs found in <path>",
                               description=("Get a key collected from "
                                            "different YAMLs"))
+        subparsers.add_parser('add-key',
+                              parents=[key_parser, add_value_parser,
+                                       path_parser, verbose_parser,
+                                       merge_parser],
+                              help="Find a key in YAMLs found in <path>",
+                              description=("Get a key collected from "
+                                           "different YAMLs"))
         subparsers.add_parser('del-key',
                               parents=[key_parser, path_parser,
                                        verbose_parser],
diff --git a/reclass_tools/create_inventory.py b/reclass_tools/create_inventory.py
index a8e048b..8bb5840 100644
--- a/reclass_tools/create_inventory.py
+++ b/reclass_tools/create_inventory.py
@@ -1,13 +1,25 @@
-import yaml
-import json
-import sys
+#    Copyright 2013 - 2017 Mirantis, Inc.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
 
-from cookiecutter import generate
+import sys
+import yaml
+
 from cookiecutter.exceptions import UndefinedVariableInTemplate
+from cookiecutter import generate
 
 from reclass_tools import helpers
 from reclass_tools import reclass_models
-from reclass_tools import walk_models
 
 
 def create_inventory_context(domain=None, keys=None):
@@ -35,10 +47,12 @@
     """
     inventory = reclass_models.inventory_list(domain=domain)
     vcp_list = reclass_models.vcp_list(domain=domain, inventory=inventory)
-    reclass_storage = reclass_models.reclass_storage(domain=domain, inventory=inventory)
+    reclass_storage = reclass_models.reclass_storage(domain=domain,
+                                                     inventory=inventory)
 
     if domain is None:
-        sys.exit("Error: please specify a domain name from: \n{}".format('\n'.join(reclass_storage.keys())))
+        sys.exit("Error: please specify a domain name from: \n{}"
+                 .format('\n'.join(reclass_storage.keys())))
 
     for storage_domain, storage_nodes in reclass_storage.items():
         if storage_domain != domain:
@@ -46,7 +60,8 @@
 
         current_cluster_nodes = {}
         for storage_node_name, storage_node in storage_nodes.items():
-            inventory_node_name = "{0}.{1}".format(storage_node['name'], storage_node['domain'])
+            inventory_node_name = "{0}.{1}".format(storage_node['name'],
+                                                   storage_node['domain'])
             current_cluster_nodes[inventory_node_name] = {
                 'name': storage_node['name'],
                 'reclass_storage_name': storage_node_name,
@@ -56,7 +71,8 @@
 
             if (storage_node['name'], storage_node['domain']) in vcp_list:
                 # Add role 'vcp' to mark the VM nodes.
-                current_cluster_nodes[inventory_node_name]['roles'].append('vcp')
+                current_cluster_nodes[
+                    inventory_node_name]['roles'].append('vcp')
 
             if keys:
                 # Dump specified parameters for the node
@@ -68,7 +84,10 @@
                     key_path = key.split('.')
                     reclass_key = helpers.get_nested_key(node, path=key_path)
                     if reclass_key:
-                        helpers.create_nested_key(current_cluster_nodes[inventory_node_name], path=key_path, value=reclass_key)
+                        helpers.create_nested_key(
+                            current_cluster_nodes[inventory_node_name],
+                            path=key_path,
+                            value=reclass_key)
 
         current_underlay_context = {
             'cookiecutter': {
@@ -131,6 +150,7 @@
             undefined_err.context,
             default_flow_style=False
         )
-        print('='*15 + ' Context: '+ '='*15 + '\n{}'.format(context_str) + '='*40)
+        print('=' * 15 + ' Context: ' + '=' * 15 +
+              '\n{}'.format(context_str) + '='*40)
         print('>>> {}'.format(undefined_err.message))
         sys.exit('>>> Error message: {}'.format(undefined_err.error.message))
diff --git a/reclass_tools/helpers.py b/reclass_tools/helpers.py
index 322ac71..7ba9d2b 100644
--- a/reclass_tools/helpers.py
+++ b/reclass_tools/helpers.py
@@ -1,5 +1,19 @@
-import os
+#    Copyright 2013 - 2017 Mirantis, Inc.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
 import json
+import os
 import yaml
 
 
@@ -69,7 +83,8 @@
     - Merges dicts and lists
     - If a dict key has the suffix '__overwrite__' and boolean value,
       then the key is assumed as a special keyword for merging:
-      <key>__overwrite__: True   #  Overwrite the existing <key> content with <key> from obj_2
+      <key>__overwrite__: True   #  Overwrite the existing <key> content
+                                 #  with <key> from obj_2
       <key>__overwrite__: False  #  Keep the existing <key> content from obj_1
 
 
@@ -122,7 +137,8 @@
           }
         }
 
-      Case #3: Use <key>__overwrite__: False to skip merging key if already exists
+      Case #3: Use <key>__overwrite__: False to skip merging key
+               if already exists
 
         dict_a = {
           'host': '1.1.1.1'
@@ -160,9 +176,9 @@
                 result[key] = value
             else:
                 overwrite_key = key + '__overwrite__'
-                if overwrite_key in obj_2 and obj_2[overwrite_key] == True:
+                if overwrite_key in obj_2 and obj_2[overwrite_key] is True:
                     result[key] = obj_2[key]
-                elif overwrite_key in obj_2 and obj_2[overwrite_key] == False:
+                elif overwrite_key in obj_2 and obj_2[overwrite_key] is False:
                     result[key] = value
                 else:
                     result[key] = merge_nested_objects(value, obj_2[key])
diff --git a/reclass_tools/reclass_models.py b/reclass_tools/reclass_models.py
index 7ebb1f3..4f85e5e 100644
--- a/reclass_tools/reclass_models.py
+++ b/reclass_tools/reclass_models.py
@@ -1,11 +1,25 @@
+#    Copyright 2013 - 2017 Mirantis, Inc.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
 import reclass
-from reclass.adapters import salt as reclass_salt
+# from reclass.adapters import salt as reclass_salt
 from reclass import config as reclass_config
 from reclass import core as reclass_core
 
 from reclass_tools import helpers
-#import salt.cli.call
-#import salt.cli.caller
+# import salt.cli.call
+# import salt.cli.caller
 
 
 def get_core():
@@ -23,23 +37,24 @@
     return reclass_core.Core(storage, None, None)
 
 
-#def get_minion_domain():
-#    """Try to get domain from the local salt minion"""
-#    client = salt.cli.call.SaltCall()
-#    client.parse_args(args=['pillar.items'])
-#    caller = salt.cli.caller.Caller.factory(client.config)
-#    result = caller.call()
-#    # Warning! There is a model-related parameter
-#    # TODO: move the path to the parameter to a settings/defaults
-#    domain = result['return']['_param']['cluster_domain']
-#    return domain
+# def get_minion_domain():
+#     """Try to get domain from the local salt minion"""
+#     client = salt.cli.call.SaltCall()
+#     client.parse_args(args=['pillar.items'])
+#     caller = salt.cli.caller.Caller.factory(client.config)
+#     result = caller.call()
+#     # Warning! There is a model-related parameter
+#     # TODO(ddmitriev): move the path to the parameter to a settings/defaults
+#     domain = result['return']['_param']['cluster_domain']
+#     return domain
 
 
 def inventory_list(domain=None):
     core = get_core()
     inventory = core.inventory()['nodes']
     if domain is not None:
-        inventory = {key:val for (key, val) in inventory.items() if key.endswith(domain)}
+        inventory = {key: val for (key, val) in inventory.items()
+                     if key.endswith(domain)}
     return inventory
 
 
@@ -65,9 +80,12 @@
         vcp_nodes = helpers.get_nested_key(node, path=vcp_path)
         if vcp_nodes is not None:
             for vcp_node_name, vcp_node in vcp_nodes.items():
-                vcp_node_names.add((vcp_node['name'], helpers.get_nested_key(node, path=domain_path)))
+                vcp_node_names.add((
+                    vcp_node['name'],
+                    helpers.get_nested_key(node, path=domain_path)))
     return vcp_node_names
 
+
 def reclass_storage(domain=None, inventory=None):
     """List VCP node names
 
@@ -77,12 +95,12 @@
     inventory = inventory or inventory_list(domain=domain)
     storage_path = 'parameters.reclass.storage.node'.split('.')
 
-    result = dict()
+    res = dict()
     for node_name, node in inventory.items():
         storage_nodes = helpers.get_nested_key(node, path=storage_path)
         if storage_nodes is not None:
             for storage_node_name, storage_node in storage_nodes.items():
-                if storage_node['domain'] not in result:
-                    result[storage_node['domain']] = dict()
-                result[storage_node['domain']][storage_node_name] = storage_node
-    return result
+                if storage_node['domain'] not in res:
+                    res[storage_node['domain']] = dict()
+                res[storage_node['domain']][storage_node_name] = storage_node
+    return res
diff --git a/reclass_tools/walk_models.py b/reclass_tools/walk_models.py
index 8b4d91f..0a66033 100644
--- a/reclass_tools/walk_models.py
+++ b/reclass_tools/walk_models.py
@@ -1,11 +1,20 @@
+#    Copyright 2013 - 2017 Mirantis, Inc.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
 
-import copy
-import hashlib
+# import copy
 import os
-import re
-import tarfile
 
-import urllib2
 import yaml
 
 from reclass_tools import helpers
@@ -20,7 +29,7 @@
     if isdir:
         for dirName, subdirList, fileList in walker:
             for filename in fileList:
-                filepath = os.path.join(dirName,filename)
+                filepath = os.path.join(dirName, filename)
                 if verbose:
                     print (prefix + filepath)
                 with OpenFile(filepath, opener) as log:
@@ -32,12 +41,12 @@
             yield (log)
 
 
-#def yaml_read(yaml_file):
-#    if os.path.isfile(yaml_file):
-#        with open(yaml_file, 'r') as f:
-#            return yaml.load(f)
-#    else:
-#        print("\'{}\' is not a file!".format(yaml_file))
+# def yaml_read(yaml_file):
+#     if os.path.isfile(yaml_file):
+#         with open(yaml_file, 'r') as f:
+#             return yaml.load(f)
+#     else:
+#         print("\'{}\' is not a file!".format(yaml_file))
 
 
 class OpenFile(object):
@@ -53,14 +62,14 @@
 
     def get_parser(self):
         parsers = {'/lastlog': self.fake_parser,
-                    '/wtmp': self.fake_parser,
-                    '/btmp': self.fake_parser,
-                    '/atop.log': self.fake_parser,
-                    '/atop_': self.fake_parser,
-                    '/atop_current': self.fake_parser,
-                    '/supervisord.log': self.docker_parser,
-                    '.gz': self.gz_parser,
-                    '.bz2': self.gz_parser,
+                   '/wtmp': self.fake_parser,
+                   '/btmp': self.fake_parser,
+                   '/atop.log': self.fake_parser,
+                   '/atop_': self.fake_parser,
+                   '/atop_current': self.fake_parser,
+                   '/supervisord.log': self.docker_parser,
+                   '.gz': self.gz_parser,
+                   '.bz2': self.gz_parser,
                    }
         for w in parsers.keys():
             if w in self.fname:
@@ -73,7 +82,7 @@
             print("Error opening file {0}: {1}".format(self.fname, e))
             if self.fobj:
                 self.fobj.close()
-            self.fobj =  None
+            self.fobj = None
             self.readlines = self.fake_parser
 
     def plaintext_parser(self):
@@ -113,7 +122,9 @@
                 model = helpers.yaml_read(log.fname)
                 if model is not None:
                     # Collect all params from the models
-                    _param = helpers.get_nested_key(model, ['parameters', '_param'])
+                    _param = helpers.get_nested_key(
+                        model,
+                        ['parameters', '_param'])
                     if _param:
                         for key, val in _param.items():
                             if key in _params:
@@ -125,6 +136,60 @@
     return _params
 
 
+def add_reclass_parameter(paths, key, value, verbose=False, merge=False):
+    """Add a value to the specified key to all the files in the paths
+
+    if merge=False (default):
+      - new value replaces previous key content completely.
+
+    if merge=True:
+      - if the specified key type is list, then value will be appended
+        to the list. Value examples:
+          '1000'
+          'new_lab_name'
+          'cluster.virtual_cluster_name.infra'
+          'http://archive.ubuntu.com'
+          '[a, b, c]'   # a list in the list
+          '{a:1, b:2, c:3}' # a dict in the list
+      - if the specified key type is an existing dict, then the dict
+        will be extended with the dict in the value. Value example:
+          '{address: 192.168.1.1, netmask: 255.255.255.0}'
+
+    - If the specified key type is string/int/bool - it will replace previous
+      value
+    """
+    add_key = key.split('.')
+
+    for path in paths:
+        for fyml in walkfiles(path, verbose=verbose):
+            if fyml.fname.endswith('.yml'):
+                model = helpers.yaml_read(fyml.fname)
+                if model is not None:
+
+                    nested_key = helpers.get_nested_key(model, add_key)
+                    if nested_key:
+                        if merge is False:
+                            nested_key = value
+                        else:
+                            if type(nested_key) is list:
+                                nested_key.append(value)
+                            elif type(nested_key) is dict:
+                                nested_key.update(value)
+                            else:
+                                helpers.create_nested_key(model, path=add_key,
+                                                          value=value)
+                    else:
+                        helpers.create_nested_key(model, path=add_key,
+                                                  value=value)
+
+                    with open(fyml.fname, 'w') as f:
+                        f.write(
+                            yaml.dump(
+                                model, default_flow_style=False
+                            )
+                        )
+
+
 def remove_reclass_parameter(paths, key,
                              verbose=False,
                              pretend=False):
@@ -135,7 +200,7 @@
     :rtype dict: { 'file path': {nested_key}, ...}
     """
     remove_key = key.split('.')
-    found_keys = {}
+    # found_keys = {}
 
     for path in paths:
         for fyml in walkfiles(path, verbose=verbose):
@@ -146,15 +211,17 @@
                     # Clear linux.network.interfaces
                     nested_key = helpers.get_nested_key(model, remove_key)
                     if nested_key:
-                        found_keys[fyml.fname] = copy.deepcopy(nested_key)
+                        # found_keys[fyml.fname] = copy.deepcopy(nested_key)
                         if pretend:
-                            print("\n---\n# Found {0} in {1}".format('.'.join(remove_key),
-                                                                   fyml.fname))
-                            print(yaml.dump(nested_key, default_flow_style=False))
+                            print("\n---\n# Found {0} in {1}"
+                                  .format('.'.join(remove_key), fyml.fname))
+                            print(yaml.dump(nested_key,
+                                            default_flow_style=False))
                         else:
-                            print("\n---\n# Removing {0} from {1}".format('.'.join(remove_key),
-                                                                   fyml.fname))
-                            print(yaml.dump(nested_key, default_flow_style=False))
+                            print("\n---\n# Removing {0} from {1}"
+                                  .format('.'.join(remove_key), fyml.fname))
+                            print(yaml.dump(nested_key,
+                                            default_flow_style=False))
 
                             helpers.remove_nested_key(model, remove_key)
 
@@ -164,4 +231,4 @@
                                         model, default_flow_style=False
                                     )
                                 )
-    return found_keys
+    # return found_keys