During my time with the game, I have sometimes gotten covers that I wasn’t ready for. For example I’ve sold dozens of 4-stars, because my 3-stars needed roster spots more. I was thinking that it could be a cool feature to downgrade a cover to a one or more lesser tier covers. Of course this feature would have to be 100 % accident proof. 
I love this idea. Especially if you earn a vaulted 4* from PVE/PVP that you won’t see any other covers until they rotate through again