Change GUID after migration (Outlook 2003)

[Blinkiz]

Hello
Am trying to migrate accounts from Zimbra 5.x NE to Zimbra 6.x NE.
Actually, am running it as a split domain, but this is not important for my problem.

1. Create new account on secondary server.
2. Export account from web client gui.
3. Import account from within web client gui.
4. Upgrade Outlook connector to new version.
5. Change account settings in outlook to point to the new server.

The last step in Outlook 2003, is to change settings so it connects to the new MAPI server. Problem is that I get an error message saying that the GUID is wrong.
Okay, I can just remove the local account and recreate, but the mailboxes is +10GB, so it will take forever for Outlook to download all the emails account. It would be so easy if I can change this GUID so Outlook will think it's the same account. Is it possible?

EDIT:
Maybe changing GUID is not the solution?
The Outlook 2003 machines already have a zimbra.zdb file that contain some sort of GUID. Maybe I can solve it in another way?