There might be soem method to reset diamonds. I remeber that when I boosted weapon kills with friend it happend to me few times but don't know exact conditions...
Anyway I noticed that soonest you can get eneough diamonds to fill all slots is lev 19 so if you go below it by geting lot negative xp (which using slash/revive method isn't hard - over 7k xp per match that means 5500 negative one) so maybe it's possible. I'm lev 20 with 260k XP so definately check it when people join my revives sessions on TA
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