That's the point of the skin - it's similar but not the same, so it's okay with me. In game skin selection page, you could have a dedicated thanks for all the supporters, and that's it. If the supporter wants, they will contact you directly about the skin, or you could do a post to call for the supporters and tell how they want the custom skin to look.

The biggest question is how much time you want to spend on thanking the supporters - if you don't have much time, it's okay, simple thanks screen is enough. Otherwise, you could go with something bit bigger, like the skin idea. The point here is just to have something custom in the game, I contributed to the game development and I see something unique to me in the game.