So just some information based on me unpacking the files. Some might find this useful. I was about unpacking interface files to forward a fix for not being capable of rebinding keys to numpad, then I decided to unpack all files, then I figured it would probably be kind to let anyone know which file types you have to deal with, regarding Mods.

Meshes come as to be expected in .nif format

Music and Sounds comes in .xwm and .wav format so I think it's entirely editable with Skyrim tools

Interface and Programs files come in .swf format, coded with CS 4.0, so they probably used the same set of tools as in Skyrim...heard that Schlangster...it's CS4...

Scripts are .pex, so Papyrus for the win!

Voice files come in .fuz format, so they are entirely editable with Skyrim tools I think?

Textures as usual, just as video files