I extracted the default skin and I'm posting it here so anyone who wants to edit it can do so. Since there is a skins folder, I have to assume the creators of the game intend people to do this. Just drop the folder in your skins directory, rename it something, and edit away.

Truth is that you could technically edit all the art in the game. I'm rather surprised more of it isn't editable now that I've seen the setup. Most everything is a png file so it would be simple enough to toss them all in the skins directory.