If I'm dropping dough on the event loot boxes, I would like to be able to REROLL EVERYTHING

just spent money on 3 sets of the event boxes (15 capsules total) for a chance to get gemstones or the hextech kogmaw skin. what I noticed is that if I get a skin for a champion I have it automatically adds it to my champion. I don't care if I got pentakill morde or the ultimate lux skin, I want to reroll them for a chance for hextech kogmaw. I don't care about anything but to be able to get the skin I want. let me reroll EVERYTHING.

edit; I also want to be able to reroll permanent skins that I have champions for. for example I rerolled 3 , got royal guard fiora (have the champion) but I don't want it to be added to my skins. I want to reroll that one as well

edit; out of 15 capsules I only got 2 gems. thanks riot for the supposed increased chances of getting hextech gem/skins