Originally Posted by Moonshine

The ‘email address as shown on the Title Bar' when you are logged in, is easily changed by a Registry edit.
Click the image below to see a short video of how I have changed the showing name (previously changed) to another new name.



The ‘path’ I have used is Copy the above and paste it into the Registry Editor Address Bar and press the Enter key.
Click the key below Identities key. It will have letters and numbers in the name.
Look for the FriendlyName entry in the right pane.
D/clicking the entry shows the current name and simply changing that name to one of your choice is done in the ‘Edit String’ dialog box.
It is wise to Export a Key before and changes are made so the original key can be Imported back should there be an unlikely issue. I have shown how in the video.