Changing record visibility with workflow

Hello guys,

We are using custom made solution called deal tracker similar to Opportunities . We also got a team of people (one Business unit) who are creating those Deals records. Most of  the records should be visible to all the team members, however some need to be hidden for other people (lets call them Group A) and visible only to team admins and Group B of the same team (until they change the deal Rating). Once the deal rating hits some level than it could be made visible to Group A too. 

I was about to create some workflow with condition of Rating level which changes the record owner to newly created team called "Group A" however I need to retain the record owner of the person who created the record for the reporting purposes, so its not solution. Any ideas please?