A gift from Riot

So I had opened up the LoL client, and what pops in front of me is a reward from Riot. They say because of my sportsmanship, I have received Heart-seeker Vayne Skin. Now this is awesome and I find it a really good way of encouraging players to be better in the community, but I don't play Vayne all too much. Now this may seem greedy, and selfish, but I would have loved the new Blood Moon skin for Elise. I really do enjoy the fact that Riot went out of their way to gift me this, but is there a way to return it for another? I know this sounds bad, and i'm cringing as I type what i'm thinking, but is there a way to switch skins? If not, no big deal (I'll just start playing Vayne a lot more), but if there is I would really enjoy another Champion Skin.

Thank you