Hey tboyes, see RIM's articles:
If you're using Exchange BES, use this article: KB10278 - Perform a Knife-Edge Cutover of BlackBerry Enterprise Server 4.0 and 4.1
If you're using Domino BES, use this article: KB-04261 - How To - Perform a cutover to another BlackBerry Enterprise Server
For such cutovers, users will not need to re-activate their Blackberry as the database that holds whatever "keys" for them to work and the server's and user's data are still the same and untouched. Re-activation is only necessary if you move users between BES servers not using the same configuration database.
RIM Support Tech Knowledge Center is many good resources, I would encourage you to search in it. Good luck!