Sometimes you may want to change the username of a synced user in Office365. Well normally in a synced environment this would not be possible:

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Luckily we have Powershell at our disposal. Just connect to your Office365 tennant and execute by running the following commands:

Connect-MsolService
Set-MsolUserPrincipalName -UserPrincipalName oldusername@domain.com -NewUserPrincipalName newuser@domain.com