Exchange Online: Change Primary SMTP Address without changing Sign-In address
By default, when you mail-enable a user, that user will be given an e-mail address that matches the user’s online services id. You can always add other e-mail addresses, using Exchange Control Panel:
As you can see, it is not possible to change the primary e-mail address using this Exchange Control Panel, when you change the user its online services id, the primary e-mail address will match the new online services id… so:
Question
Is it possible to change the primary e-mail address of a user without changing it’s online services id?
Answer
Yes, by looking here:
You can see that by using the Exchange Shell, it’s fairly easy to change the primary e-mail address without changing the Microsoft online services id.
But….isn’t there an easier way?
And, yes there is…using the Exchange Management Console
You can install the Exchange Management tools on a Windows 7, as described here: Install the Exchange 2010 Management Tools
http://technet.microsoft.com/en-us/library/bb232090.aspx
After installing the required windows components, I am ready to Retry:
When launching the Exchange Management Console, I get an error that he is unable to connect to an On Premises Exchange environment, but I can right-click and select Add Exchange Forest:
And chose to select to Exchange Online:
And there I can see the mailboxes in my Online environment:
When going to the properties of my mailbox, I can select the tab E-Mail Addresses,
click on ilse@vancriekinge.be, and click Set as Reply:
Time to test:
Primary E-Mail address has changed, and the Online Services id hasn’t 
Ilse