[CentOS] Forced upgrade to 4.3 ?

I have Centos 4.2 and I run yum update periodically and manually when security patches are released, etc. Today I saw the sendmail security update and although I don't use sendmail (I use Postfix) I ran "yum update" and got a huge list of 93 packages to update. I presume this is to upgrade to 4.3. As this is a production server I'm nervous about doing an update that big.

Is there a way to not go to 4.3, or should I just go on and load it? I have a few packages I loaded from source, all related to my mail system (dcc, razor, amavisd-new, spamassassin). I'm worried about the 4.3 update hosing those.

Thanks, Scott