You can't choose what mastery emote you want.
What if I want to have level 4 lulu but I'm actually level 5.
What if I want to have level 4 lulu but I'm actually level 5.
I know the pain. Not that example as it doesn't make sense, but I almost have Zyra to lvl 7, but the lvl 6 banner matches her Dragon sorceress skin so well...