I brought up this topic in the Discord's tagging channel for a brief discussion, but I think it's worth bringing up in the forum as a proposed change. Looking through the tags for gacha games (Azur Lane, Fate/Grand Order, Arknights), there's a pretty clear convention of tagging alternate costumes as character_(costume)_(copyright) (eg. Bremerton (Kung Fu Cruiser) (Azur Lane) or Blue Poison (Shoal Beat) (Arknights).
However, if you look at the tags for western games with a plethora of alts (League of Legends, Overwatch, Apex Legends), they're primarily tagged as costume_character (eg. K/DA Akali or Cyber Punked Wattson), and even a rare few cases where the costume name is entirely different from the character name such as the Soldier: 1776 skin for Soldier: 76 (Overwatch). For the sake of uniformity, I think it may be better that we rename the skin tags for these copyrights (and any others I missed with tags like that) to match the other convention.
If the idea is overall favorably received, then I'll set up a BUR for the Apex tags later today and try to do as much of the Overwatch ones as I can. I'll leave LoL to someone more knowledgeable on the game since I really don't know much about it, plus it's going through its own tagging overhaul in topic #18782, so it'd probably be best to wait until those changes are done before updating.