I want to release a video tutorial later on, after we've hopefully heard something about modding support. Probably Larian will be releasing videos and documentation on what I'd be describing. I may put together a tutorial template kind of thing for people to play with, but I'm also kind of leery of that, since that will be out of date by next patch. Kind of in wait and see mode right now.
The basic concept is to use the .pak
extractor from the old game. Most important stuff is in the Origins.pak and Shared.pak. Look through the files and see what Larian did (and you can look through my mod and see my crappy scripting). Script files can be opened with text editors. Use Notepad++ or another good text editor.
Making mods is a matter of taking the files that you extract, and making folders in your game directory that match the same directory path of the files you want to modify (or add). So with my mod, you can see I created a bunch of folders, like the stats folders and stuff.