docs: def modify_agent_property(self, agent_id, key, value):
          '''
          modify_agent_property(self, agent_id, key, value)
  
          Modifies a single single property of an agent. If the property does not exists then it is created as a custom property.
  
          :Parameters:
          * *agent_id* (`string`) -- Identifier of an existing agent
          * *key* (`string`) -- Key of a property to change
          * *value* (`string`) -- New Value of the property to change
  
          :Example:
          .. code-block:: python
  
             opereto_client.modify_agent_property('my_agent_id', 'agent_new_property', 'agent value')
  
          '''
          return self._call_rest_api('post', '/agents/'+agent_id+'/properties', data={key: value}, error='Failed to modify agent [%s] property [%s]'%(agent_id,key))