It will be interchangeable. You can swap advancements, as you put it, at any time just as you can swap classes. You will just need to redistribute points. SE just has to not put a penalty on switching like stats is now. I think to fully change your stats at 50 it takes like 7 hours... Thats completely absurd. If I wanna go from tank to damage dealer on the same class or different class I will do it when I please.