I don't just insert my textures into BrawlBox... I always test them in 3DS Max first. Here's my method...
What you'll need...
First, open your folder with all the fighter folders.
I'll be editing Mario, so ill open his folder.
Export all the textures from the .pac
Export the ModelData[0]
Save in the same folder as the textures
Convert the ModelData to .dae using AIS.
Edit the textures to your liking and save.
Import the dae to 3ds max using collada and use the following options.
Run MK's Script
Press Fix Ais import on MK's script.
This is the Model all textured you don't have to do anything else.
If you like it, you can just replace the texture in BrawlBox like usual. Major credit to MarioKart64n for the script!