Looking at CVS and it looks like you can create a CVS branch when ever you want.
Tag is FOO_BARa
And its whats live on the servers and we need to patch a file or 2
You can run
cvs rtag -b -r FOO_BARa FOO_BARa_branch mainsite
And it will create a new branch that is based on the tag.
Then just check out the new branch add the changes and deploy it.
Technorati Tags: CVS