[CentOS] yum-priorities behavior with downgrades [was: sa-update error with perl]

Tue Jan 10 03:13:10 UTC 2012
email builder <emailbuilder88 at yahoo.com>

After solving my problem by downgrading perl-NetAddr-IP to the CentOS
repo's version, yum is of course telling me perl-NetAddr-IP is out of date
and needs to be updated (back to the buggy one in RepoForge).

So looks like yum-priorities is in order (ha! the pun!), but I have a question

>>  Hmm, OK, prioritze CentOS repo over RepoForge then will yum update

>>  figure out the rest?  I don't see any priority settings in my yum conf 
>>  files...
> 
> # yum list | grep priorities
> yum-priorities.noarch                      1.1.16-16.el5.centos        installed
> 
> # cat /etc/yum/pluginconf.d/priorities.conf 
> [main]
> enabled = 1
> check_obsoletes=1
> 
> Then add "priority=n" to the repos sections.
> n=1 for CentOS
> n=2 for repo 2
> etc...

If I already have a bunch of packages from RepoForge, some of which
might also be in the CentOS repo (some presumably with lower version
numbers), what happens after installing and configuring yum-priorities?  

Do those packages automatically get downgraded?  Does yum complain
and tell me I should downgrade?  I assume upgrades would happen per
usual if there are newer versions of packages in CentOS repo.

I'm slightly concerned because I have a handful of packages that got
installed automatically from RepoForge when I installed amavisd-new
from there, and I'd hate to break something.

Thanks for any preemptive advice!!!!