[CentOS] How do I revert back to a non-CentOSPlus install?

I installed PHP 5.0.4 from the CentOSPlus repo a week ago, but now the yum cronjob seems to have upgraded to a new kernel, a new MySQL and god knows what else. Big mistake.

How do I (safely) revert back to the stock CentOS 4.3 rpms? I want to keep PHP 5.0.4, but that's it.

Is there a cleaner way than uninstalling the rpms, editing the repo file and the (re)installing from base?

I just recently learned about the protectbase plugin, which I intend to use from here on out. The damage is done though.

This question is a repost from the forums. They sadly don't seem to recieve much traffic.

Best regards, Jens