Yeah going to have to throw my lot in with some of the seasoned modders here. So far as creating new ones...I don't know. Maybe? I seriously doubt if you could 'create' a new class--but maybe someone here could inform me otherwise?
I've only ever worked on dialog or altered the player character's appearance to something else and given him Malak's voice. More just playing around with existing tools than modding really.
I have poked around enough to find there are other classes already in the game:
Originally Posted by Canderis
Im pretty sure you can add new classes, but not force-using ones.
Hm. You mean the incomplete ones not used in the game?
Bounty Hunter being one, though can't remember the rest. This from my rusting memory of that TSL warp band mod.