As you can read in their readme file this isn't a easy thing to do. In fact you can't do it like a normal Q3 model. A fact which they have worked around by using their model to replace the James model. This is a huge job. Larger than huge, this is like a mini-mod it so large.
Some models even have a smaller download.
But they worked it out. I can't imagine what kind of perseverance these guys have, but if they can bottle it, I'll take a case. Each of the skins are now a new character you can pick in Team Arena, one for each of the clans. Try it out, you might not like it, but I doubt you'll see another effort like this again. I tell ya.