Moment to re-think my steps. That error occurred when renaming the file BEFORE I unlinked and deleted. I adopted Toy Guy’s suggestion many years ago to rename files to deleteMeXXXXX (original name) then periodically tossing them in administrative panel (web trees).
The message didn’t make sense as I don’t share the images. My A-D family tree also has switch to another tree much as my Royals and Rebbees. But I use subdirectories to keep them separate.
I can see not deleting if linked but rename should be global if in the image is in fact linked to multiple trees, I think.