I have been trying my hand at modding (NPC and kit creation) .. not going well. but i want to learn!

Im currently replaying BG1tutu at the moment. So to start out small, I was wondering if it was possible to somehow get the files that script the npc's already in the game (dialogue files, soundsets, etc. ) and basically rewrite them to create a new character.
So for example get the files that make Ajantis (pre romance/friendship, just the basics) and use it as building blocks to create a new character. rename him, change his class, kit, history, etc. and install it as a new character in the game.
Any help would be appreciated. I've read a bunch of the tutorials and everything, just still a lil' unsure on my modding feet
