As long as the mailboxes are intact and you're going to a different Exchange Org then the BES doesn't care. With a different name you will want to make sure that the MAPI profiles on the BES can see the Exchange Server.
The IP doesn't matter as it looks by name anyways.
If the mailboxes are intact then the hidden BlackBerry folder will be ok, this folder contains their PIN/SRP/BES name/etc. If this folder is lost then you would have to reactivat the users.
To check the MAPI profiles do the follwing:
1. Open BlackBerry Server Configuration
2. Click the BlackBerry Server tab
3. Click Edit MAPI Profile and ensure that the settings are correct
4. If the settings are not correct update the Exchange server name and click Check Name
If everything resolves then your golden. If the BlackBerry Manager throws any MAPI profile errors when opening you will have to delete it from the registry and re-create it. Here are the steps:
1. Open the registry
2. Go to HKEY_Current_User\Software\Microsoft\WindowsNT\Cur rentVersion\Windows Messaging Subsystem\Profiles\
3. Delete the BlackBerry Manager profile (NOTE: This can always be used to delete and create both of the BlackBerry profiles - Server and Manager)
4. Close the Registry
5. Open the BlackBerry and click ok for the warning and enter the mailserver and mailbox name again and then click Check Name
That should cover it. You will only need to re-create the profiles if you can't open the Manager or if the profile in the BB Server Config is wrong.
Let us know if you have any more questions.