SRP Identifier + SRP Auth Key + BES Admin Account + BES Virtual Server name
keep all of those the same and you won't have any issues. you can do a fresh install, upgrade to SP5, etc. without having to worry about users having to recradle. the database contains IT Policy information, so you will want to keep that, most likely.
IP address and server name changes won't affect it, so long as you keep the BES virtual server as the same name.
but it would be smart on your part to add a disclaimer stating something along the lines of 'if you do experience any issues, recradle your handheld'...