I can tell you the reason that simply changing the flag on your save state didn't work. The characters's alternate outfits are completely different characters in the game scripts. They don't share the same event logic, and they don't appear in every area.
I noticed that there is a battle version for both casual and uniform models and a map version for both casual and uniform models. Enforcing the texture using tonberry causes the uniform to display incorrectly (eyes near the arms and skirt textures on the head, it's weird!). Is the "casual outfit" model for the characters the "alternate model"? Or it's the contrary?
The problem here is model related, as long as I can't entirely force the game to use a model, I can't do much. Isn't there a way to simply unpack/repack the file containing the model itself, replacing with the other model file?! Even if one can't open or edit said model file, replacing one file with the other should work, wouldn't it?
Thanks