I’m going to say not at all. If someone wanted to edit my illustrations for whatever reason, I’d feel better if I were contacted first, but I’ve never gotten a good feeling from finding one of my illustrations edited and/or credit removed. Part of that could be because they were complete surprises that left me feeling robbed, but I just see no reason to edit someone else’s art. I will say that asking beforehand gets rid of any disrespect, but my answer will more than likely be no.

If you are inspired by someones work or just think it would look cool another way, you can always create your own version. I’ve seen a lot of esqueleta fan art where someone would create their own purple haired esqueleta instead of editing one of mine to have purple hair instead, that seems way better to me.

Also, if the edits were some sort of collaboration that I could approve of/be involved in, I see no problem.

EDIT (lol)

If someone were to ask me permission to get one of my illustrations tattooed on them, I would not mind if they tweaked or edited the design (based on my art) for their tattoo since it is going on their body permanently.