Are you talking about the behaviors as in the code for the behaviors? Like changing/making your own behaviors? This sounds like a must for me to learn >< What programming is needed?
Also, how would you be able to mod the game and keep the original game too? Is there a mod loading UI I haven't seen?
Well I would have you learn C# because this is the language it is coded in, there is no mod loading UI and is not required at this point and yes you can still keep the original files of the game, but they need to be stored elsewhere while you use the mods (especially if the mod is located IN the assets folder, a custom assets folder if you will).
EDIT: Augh, don't mean to be such a bother, but I guess I can't get the mods moving without the behaviours and even with the new extractor I have no luck with extracting any other file except for the assets.