Nope, that's way beyond impossible sorry.
In-depth Explanation: Skins are gotten from minecraft.net whenever a player logs in OR when the server tells all the other players that a new person is joining. That's the only time your minecraft will ever download a skin for a player. However, even though it's possible to tell players that someone has joined and force them to download the skin, we can't customize what skin is download/that should be shown since it's hosted by Mojang on their servers ;D
Now I know other servers like Wynncraft make it so you have custom armor by changing your skin. That also requires hundreds of accounts with a server that's constantly manipulating the skins of players, uploading them, then downloading them again so everyone can see them. ProjectKorra is already hard enough on a server without it doing that lol. Plus, doing it EVERY time you do an ability is just RIDICULOUS.
So sorry, no, it's not, and probably will never, be possible xD
Sorry guys I felt like I had to xD