UPDATE:
Checked the lot survey/fenceline and determined we both own the tree. The light is definitely not to code, which limits height to 15 feet. This light is 32' feet up the tree.
I used a 24 ladder, tied to the tree, and stood on the top rung. No, I didn't do it like
Aerial Traveler (without a lanyard). I connected my trusty HipSTAR well before my feet were near the top of the ladder.
I didn't pull down the light. It doesn't belong to me. I just added a light shade on the side that points across the fence to my house. It's finished marine plywood, stained to match the tree and the fixture. Looks really nice actually. The light still lights up the neighbor's backyard. It just doesn't shine in mine. There is a nice crisp bright/dark separation near the fenceline.
I didn't want to piss off the new neighbors. I hear they are nice folks. They won't even be getting the house ready for another month or more, needing to sell theirs out of state. I'm getting a really nice "Lights Out for Wildlife" sign made up for the front yard. We'll see if it helps with all our neighbors who have discovered outdoor lighting with 5000 lumen LEDs.
If they take down the shade, I'll let them know in the nicest possible way that it's not acceptable. If they ignore that, I'll just have the County have them take it down altogether. I really want great neighbors and am willing to compromise a bit.