You waive by actively deciding not to enforce your rights. You just cannot divest those rights. So those who buy art cannot use contract to totally escape the artist. If you buy art, the artist retains a degree of control.

The pivotal case in canada involved a mall sculpture of some geese in flight. The mall put red bows on the geese during christmas. No dice. The original artist said that was an unacceptable change. They needed to get the artist permission before making such a change.