We cannot edit backdrops (or doors or overlays) the way we can walls and blockage.
But, I looked at the code, and I think "I" might be able to add them.
They ($Wall, $Block) are basically in the same format and it's one which I can understand.
These tools with the talk.bin have given me an idea how to do this at the zone level.
I've also come close to figuring out how to add in-game changes to the frame set. Close...