[Yum] howto revert all packages from an auxiliary repo

[Hans-Peter Jansen]

Hi,

what is the best procedure to revert (downgrade) all packages of a 
specific repo, e.g. if distri comes with KDE 3.4.0, and KDE 3.5.1 is 
available from an auxiliary repo. Upgrading is as easy as enabling this 
repo and running "yum update", you all know. Now considering, that 
there are some unacceptable bugs, I wanted to revert to the base 
packages. 

Manually running "rpm --oldpackage" with all previously updated packages 
and their dependencies is a tedious task (given, they're scattered over 
several repos..). Anything yum can offer to ease that unfortunate 
exercise? 

Pete