[DiapDealer]

eschwartz is correct. No internal filenames in an AZW3. No "files" at all in an AZW3. Just records in a binary database. calibre-edit just unpacks the binary into an oebps type structure that makes it easy to edit. Any filenames are manufactured by calibre-edit and will be re-manufactured each time the AZW3 is unpacked for editing. I'm guessing the latest update stopped allowing you to rename the files because it's pointless to do so--broken links or not.

Also, new html files are created by calibre-edit from the internal kindle markup contained in the AZW3 each time it's edited (and turned back into proprietary markup when it's saved).

The thing to remember about "editing" AZW3s is that they're not epubs with "files" that can be simply edited and saved. What you are actually doing is creating new source code, editing that, and then recompiling that source code back into a proprietary binary file each and every time you edit.