Mendalism
This is a word that essentially means "un-doing vandalism". Except that it's not just cleaning up something, such as wiping graffiti off a wall, or restoring a weather-beaten outside mural. The key is that, just like vandalism, the act is done without permission.
It's like vandalism only with the word "mend" stuck in there.
As I understand it, the intent is good and not evil. As opposed to vandalism, which is done with intent to harm or damage. Mendalism is done with the purpose of doing something good. Like "mending" something. It's just that you don't have permission to do this.
