Thanks guys! I'll give it a try
Although, if I just overwrite the file (In this case it's the Immortal skin that I want to modify and use on the Berserker unit), won't this change the default berserker skin into the Immortal skin I use? I want it to just change for the Amurite Civ.
You should use GIMP with dds plugin; it's in the tutorial. It lets you edit certain parts.
Example: Copy the clothing you want from one file, and paste it over the dds file that the nif is linking to.
I'll see what I can find...
EDIT: It seems the Berserker and Immortal skins are radically different. That means more work...