Hi,
This implies that "all you have is a hammer" but you can already run "yum history undo".
which works up to a point. If the older pkgs you had prior to an update are not available anywhere history undo isn't going to be able to 'undo' but so much.
And of course, it's not going to work if Rawhide's broken something anywhere in the yum/rpm/*kit/etc stack, or if prelink's hosed every binary on your system again, or so on. But this would.
- Chris.