Backing up system binaries and non-user-editable configuration files is not standard practice on Linux. The assumption is, the updates are tested and work well, so there is minimal risk in applying updates. On the other hand, if the updates happen to break something, the system won't be bootable/usable and you'll have to do some manual data recovery by mounting the drive in another system or booting from another OS anyway. You do back up your sensitive non-replaceable data (i.e., all data on the OS other than things you can replace easily as a free download), right? :)
If you insist on backing up the operating system files, there are robust backup solutions such as Amanda and Bacula. But there's no simple, foolproof way to back up yum transactions and revert them on command. Especially since
yum likes to occasionally clean up its rpm cache, so over time you lose old versions of rpms that are obsolete. This is done to save disk space.