Single post in Public-use Site Skin Directory - Add yours?

Hello~! I had a question pertaining to site skins, so I figured I'd post it here? Right now I'm using one of the Official Site Skins, (Day of the Dead - Xerneas) and I'd like to add some code to it for the type race to make some eggs in the shelter stand out, but I realized you can't really edit the Official Skins. Is there a way to do that? A list of all the color codes used where, or just an option I'm not seeing?