I'm in a similar situation, and I can safely say that at minimum it's a huge pain in the ass. I'm trying to make a mod to give arcane tricksters "Pilfer Magic" a la NWN2, as I feel they're just underwhelming and I want something to make them a little more unique and powerful, and I've been hacking away at it for several hours and all I've finally managed to accomplish is pulling up the game files with dnspy.