True, my Electromesh Robes mod adds 2 new item files with new textures but they use the vanilla knight and master models. Replace those and things won't line up. I have used the slot for the Revan/Star Forge model (modelj in appearance.2da -> PMBJM/PFBJM) to introduce models that are not yet used by player outfits and still leave existing gear intact, but it's not without issues. For one, in vanilla all the female entries (texj) point to the male texture, you would have to change that to make that slot more useable. After adjusting that you could overwrite the Revan/Star Forge model with either the knight or master model (there's no "fix" for more than 1), edit one of the Electromesh item files so that they use the Revan armor base item, adjust texture and icon filenames. A lot of work for one mod and there will still be some issues that I don't understand myself yet. If you're looking for a modding challenge then give it a try. I think you're doing good on understanding how things work for someone that calls himself someone with little experience.
Edit: wrote this before your post above.