Can you give me an example file location and character you've changed?Yes, i do!
To do that, you have to find the directory of the defaut costume for the char that you want change, find files for the costume you want to use, name "xxx_02" for the first DLC costume, or "xxx_3" for the secons alternate costume... and rename all the same number files in "xxx_01" and replace the original "xxx_01" files.
The alternate costume begins the defaut costume!