Change Display Name in Office 365 Synced Active Directory

After installing office 365 for all the users and syncing the directory I found that the display name of a user was misspelled.   There was a lot of confusing information on google including to use AzureADPreview module in powershell.  This did not work as one cannot change the attributes in Azure AD if you are using directory sync.

First you need to make the changes in your on premise AD.  .  

Open active directory Users and computers

In the menu on the top, click View and click on "Show Advanced Features" ( or do nothing if checked)

Open the properties of the user to be edited.  Click on Attribute editor.  Change the values of both 

cn

displayName 

to the new value.  Click Ok 

Right click on the User object in the explorer pane and click on 'refresh'.  Check that the user was indeed updated.  

displayName is not a property synced by default by Azure AD Connect, so you have to add a new rule to the synchronization editor of Azure AD Connect.  The following link explains how to add the rule:

https://docs.microsoft.com/en-us/azure/active-directory/connect/active-directory-aadconnectsync-change-the-configuration.

In brief one needs to 

Stop the AD Sync Service

Create a rule with the "Synchronization Rules Editor"

(Add a new rule for users which syncs the displayName to AD).

Open Azure AD Connect and resync.  

The user may need to logon once or twice for it to show up.  I didn't have to reinstall outlook 2016, the display name updated on its own.