You can do this now when you design them.
I typically make a 'Command Guardian' which is a medium hull with lots of defense and my weapon of choice. It will never leave the command ship (support) but will engage any 'escorts' or assault ships that try to get past my capitals and other assaults.
I also designate Assault ships and combine them with Capitals. This really makes for a good combo. My carriers I designate as support to 'hang' back. Prior to this update they were set at assault and charged forward and DIED.
Are you asking to designate what role is what prior to battle?