I'm guessing this has more to do with Jabber than Zimbra, but here is the problem.

Someone requested a name change (marriage), so I went into the Zimbra Admin Console and changed their email address (firstname.lastname) and had them change their email address in Outlook. All was fine until they went to IM in pidgin. So I had them change that address, too, but none of their contacts are there.

The contacts are still there, but the new email address is no longer authorized with any of the "buddies" clients. Is there a way to fix this without having to re-authorize every buddy on their list?

It's not a big hassle right now, because they only have 20-30 buddies, but it could be a big issue in the future.