As topic title says, do you think the mutant tag should be categorized as a species tag instead of a general tag?

Nah, if we can notice the original species, we tag the species and then mutant, just like we do with hybrid, tagging the apparent species and then putting hybrid, if we don't have a clue about what spawned it, we tag unknown_species

It should definitely be categorized as species (a red colored tag)

Don't get me started on that tag.
I've been meaning to clean it up, because it's full of characters from Teenage Mutant Ninja Turtle, thanks to that one tagger who I constantly complain about. You can't see that they're mutants, so they shouldn't be tagged as such.

I'm not sure how many actual mutants there are under that tag. It just doesn't mesh well with twys.

But I digress. 'Mutant' isn't exactly a species, but maybe it's related enough that we should make it a species tag anyway? After all, monster and zombie are also a species tags.

Back when the species tags were introduced and the types were being changed I included a bunch of broad tags like monster, robot, hybrid, unknown_species, spirit, etc.

https://e621.net/forum/show/45279

My original list included mutant but I see that it's not crossed out. I'd change it myself but it says only mods can change tags with 100+.