True that, the multiple texture upload section doesnt work for me and I have to change over 30 textures when I want a new look.
I'm gonna try to explain it better,
Add something where you can combine different images for each texture, save it.
After saving it you could have like an "item" which you'd basically click to upload all of the images to the specific textures.
Uploading them 1 by 1 kills so many time.