As of right now, the way sticker mastery works requires you to place 10 of any one sticker to master it, hence allowing you to use it as a reaction. In GameJolt terms, each sticker counts as "10xp" with the total xp required being 100xp (The formula being 10x = 100). I feel like adding a bonus amount of xp gained per charged sticker would make people want to place charged stickers more, or at the very least be a nice little bonus for those who do place charged stickers consistently. Some ideas are listed below:
1. A 25% xp bonus if charged sticker is placed (10x = 100, if x is charged, (10 x 25%)x = 100).

2. A flat amount of 10 or 25 extra xp is added onto the base amount gained (10x = 100, if x is charged, 5x = 100 or 4x = 100).

3. Different xp charge values depending on the sticker/sticker pack (10x = 100, if x = , check for charged sticker, if is charged, add 10 flat xp to base (10x + 10).

I'm sure these ideas have been suggested before, but figured I'd mention it anyways.