Você pode tentar um processo como este: link , que envolve um um pouco da edição do registro, que pode permitir que você remova a conta principal.
Texto relevante:
Remove the primary account by editing the registry
You can edit the registry to remove the primary assignment, however it is not supported and not recommended by Microsoft. If you mess up, you will need to make a new profile, restore the profile key you exported, or use System Restore to go back to a previous restore point.
Close Outlook and open the registry editor.
Press Windows key + R to open the Run command then type regedit in the Run field and press Enter.
Tip: Export the profile key before editing, so you can recover your profile if you make a mistake.
To remove the Outlook 2010 primary account from the registry, go to the profile key:
HKEY_CURRENT_USER\Software\Microsoft\Windows NT\Current Version\Windows Messaging SubSystem\Profile\profile-name
In Outlook 2013, the profile key moved to:
HKEY_CURRENT_USER\Software\Microsoft\Office.0\Outlook\Profiles\profile-name
Export the profile key then search for and remove one (or both) of the registry keys related to primary account.
I searched the profile for 001f662b as this value is used by each account. You'll find two keys containing this value for each account and you need to delete the second key that belongs to the primary account (you can delete both keys). Once I did this, I could delete the primary account from the profile.
Note: you need to delete the entire key (on the left side), not just the registry value. The value helps you find the right key to delete.
Na minha experiência, criar um novo perfil é a melhor opção.