I wanted to have a Common Velosotor with the older model. Since I do not own the art, or neither can buy it, would it be allowed? To have one overlay that is just an older Subeta pet, that got revamped.

Thanks for the help in advance.

Yep, you can do that with a coded overlay on your pet's profile. If you want to use it as a custom overlay though, there would have to be some form of changes made since I believe even pre-revamp art is still considered official site art

Check these posts from from this topic Custom pet overlays

I imagined as much, but still wanted to check.

so from the quote

I don't necessarily need to make any alteration, just credit the fact that it is an older art from the website and such. It's worth trying then, lovely. Thank you very much for the information!

Not having to alter it seems kinda weird to me since custom overlays have to be unique, but ¯ ¯(ツ)/¯