[CentOS] Downgrade an rpm

>Does the current installed version give a problem?
>
>Using something like rpmforge to install an rpm ( I presume you used yum
>or something?) I think the only way is to remove it, and then manually
>install the correct one. The command would be something like rpm -ivh
>http://rmpforge-website/rpms/package-1.2.3.54-234.rpm - or something

That is what I suspect. I presume I have to block it from being upgraded after as well. How can I force the new app back in without worrying about this dependency?

Thanks!
jlc