Microsoft has announced the availability of disabling either temporarily or permanently Directory Synchronization (DirSync) in Office 365, http://support.microsoft.com/kb/2619062/en-us. This is great news! in BPOS this was always available, but in Office 365 it was not possible.
Before this announcement, if you turned on DirSync in Office 365 it was permanent. While you want to ensure that DirSync is running and updating Office 365 with changes made in the on-premises Active Directory, some things needed it not running to correct errors. Some of these would be for accounts that need to have a UPN changed.
This will also enable a smaller company to "Populate" Office 365 with the accounts from on-premises Active Directory, once populated a company may choose to switch to Online IDs going forward, turning of DirSync will allow this to happen.
A Big Thanks to the Microsoft Online Services team for enabling this functionality, it is greatly appreciated!