Things that aren't hard coded are largely doable. Want to play an invoker follower of Thror, you can, want to do an A-P in Battle, you can. Want to change from Acolyte to Maran, it's as simple as a mentality change for your character from one of wanting to do more than defend, or some traumatic event caused them to want to cause less pain to others. Most will involve needing an Immortal to make them happen though.

The key to any transition is time, RP, and lining up with an IMM.