Any tricks to get Time Machine to backup from a specific date?

I recently installed Mavericks and in the process I erased my iMac's hard drive and gave the drive a new label. This seems to have thrown Time Machine into a tail spin - understandably, it now sees my iMac's hard drive as a different drive and now wants to backup the whole drive from scratch.

Before installing Mavericks I did a backup which I restored after the installation - so my files were in the same state immediately after the installation as they were just before it. This was a few days ago, so some of my files have since had some changes which need to be backed up. Is there any way I can trick Time Machine into backing up changes made only after the day I installed Mavericks? Or will I need to erase my backup drive and start again? :/

Thanks.

Edit: nevermind - it seems Time Machine somehow already decided to "clean up" my old backups, despite me having automatic backups disabled, but now gives me an error message saying my backup disk doesn't have enough space to complete a new backup. This is all despite the most recent backup available in TM is almost identical to what I have on my Mac today. So I guess I have no choice but to erase my backup drive and start again - I've already lost my 2+ years of backups.

Managing/migrating backups shouldn't be complicated, Apple. It really shouldn't.