Before making a BUR i wanted to gather others' opinions on whether this would actually help or not.
I have always found the "costume" in adapted costume and adjacent tags meaning "outfit character wouldn't usually wear", something you would wear in a convention or something.
"Outfit" has a more neutral meaning, and in my opinion rolls off the tongue better. Alternatively there would also be "Clothes".
One caveat i can already see is that it would break the consistency with tags like reindeer costume, and reindeer outfit or reindeer clothes doesn't sound right.