As far as I’m aware the only regulatory framework governing space is the Outer Space Treaty, which is more concerned with preventing military activities in space and preventing individual nations from claiming ownership of extraterrestrial territory. There’s currently no mechanism for other countries to tell NASA they can’t punch a space rock in the face.

I think there’s probably an argument to be made that some kind of international council should be established as more and more countries are starting to get into the game, but that hasn’t happened yet. I don’t think any of them would’ve objected to DART anyway.