Regarding In-Game purchases

So this may or may not be a stupid question, but Im making a game that I could potentially profit from, and an idea I had for this game was to allow switching the skybox, player color, etc within the game. I had the idea to make some skyboxes/colors only accessible if the player paid for them (I'm not the first one with this idea) and I was wondering if I could do that with certain free assets from the unity asset store, or if I would have to make my own assets to do that.