Cons: this is a bit hackish, ConstraintDescriptor attributes are supposed to be static things.

That would be my main argument as well. IMO the ConstraintDescriptor describes the static view of the constraint. You basically would get "different" descriptors depending on the current validation.

If your proposed fix works for you, I think we leave it there. If you like you could open another issue, since it seems to be independent to this one.