Im just a noob at this as well, but i think i may have a way.
Ive downloaded the file called "True Sephiroth.GMO" and didnt know how to make it the DLC 1.
What i did was go to the site "http://dissidiaforums.com/showthread.php?7956-DLC-Costume-Texturing-Is-It-Possible/page16" replace the name...