Ah, thanks. I believe I was just doing things out of order. I also need to change the directory name externally (since doing so internal to MC doesn't drag along auxiliary files like booklet.pdf), and I was changing the path name out from under MC, so to speak. If I change the directory name externally first, then let MC run Auto-Import to update its links, then change the tags, the new tags stick as I would expect.
Thanks again.