How do I downgrade an RPM on a machine without 'yum'?
rpm -Uvh --oldpackage [filename]
--oldpackage allows you to install older versions, -U means "upgrade", but in this case it will just replace the other version. If you use -i instead of -U you will end up with both versions installed.
You can also try yum downgrade packagename, depending on the version of yum on your system.