An Adoptable is a design/character sold from Artist A to Artist B. Or that's what I thought anyway.

Pretty sure that if you're selling a design for something, you wouldn't own it any more. You've SOLD IT.

I saw someone who sells an adoptable say that they weren't allowed to use the design for anything other than sport, and that anything else just wasn't allowed. No prints. Not even character tweaking.
Well.
That would be understandable if that were still your character, Artist A.
But it belongs to Artist B. They can do whatever they'd like with the design. They can tweak it. They can draw it. They can even make prints with it. It's THEIRS.
If you wanted to keep all profits with the character, you shouldn't have sold it.