A bit of ugly registry editing lets you rename the mailboxes, at least:
1. Fire up ye olde Registry Editor.
2. Fight your way to HKEY_CURRENT_USER\Software\Microsoft\Windows
NT\CurrentVersion\Windows Messaging Subsystem\Profiles\
3. Go through each key, looking for values with the name "001f3001". You'll find one for each mailbox (plus a few for other random crap).
4. Edit the value as desired.
5. Open Outlook, admire your perseverance - and curse Microsoft (again).
Credit to Ruben for this information.