From my experience with modding the old Baldur's Gate games and a few other games, I imagine that if you can edit the dialog in which you assign class to the character, you will probably find a piece of code associated with each dialog option, somewhere, with a bunch of commands that assign abilities to the character. Then all you need to do would be to replace those abilities with new ones - something along the lines of replacing "xyz_BatteringRam_xyz" with "xyz_BlitzAttack_xyz", and so on.
If you make major changes, you probably want to edit the text as well, so that it better reflects the new abilities you put in.
That being said, I've never actually tried doing any modding with this game, so can't really help you there, sorry. I think I'm too old for this stuff now.
Last edited by Try2Handing; 24/02/18 10:21 PM.