I have a directory structure with many hundreds of files and folders underneath it for organising files (in this case photos). I create backups of that directory structure by rsyncing it to identical copies on an external drives periodically. These drives may be offsite some of the time.

I want to restructure and rename the files and directories in the original and then, later, when I have an external drive onsite, be able to run some tool that will cause these structural and naming changes to happen on the backup. If I just us rsync, it'll have to recopy much of the data to the backup drive, which I'd rather avoid due to the sizes involved.

How can I get the changes I make to the original directory into the backups, as they become available, without having to recopy/rsync the data?