Duplicated Migration Roles in phased migrations

In https://jira.atlassian.com/browse/MIG-212 it was confirmed that duplication should be acceptable for drift in config. And the case was closed with the message

However, there is still a scenario when duplication can happen - if a role was migrated before, and then it was modified in server or cloud. When re-migration happens, only in this scenario will the role get duplicated. 

The merge of roles will only happen if they are 100% identical. Any drift between the roles will result in duplication. 

In phased migrations which span over months , changes can't be controlled. And a long term freeze is not possible. 

The purpose of this suggestion/enhancement request is

• Allow the user to choose whether they want the config from Server as source of truth or the previously migrated config in cloud as source of truth. And the master config should over write the cloud config . 
• Allow the user to option to choose Merger or Duplication rather than default duplication.