If you don't feel like taking things too seriously, you can puzzle ad bewilder ppl in random FATE runs by staying arcanist (i did it a few times just to see what reaction i would get... pretty funny stuff sometimes) but if you are loading duties and whatnot, you will probably raise a bitchfit and kick you from the party before you even get to try.

In the more practical sense, you'll find that SMN and SCH will feel pretty different (ESP SCH) and you'll find it hard to go back to ACN altogether.