04-24-2017 12:47 AM
Say you are registered with email@example.com and you want to use firstname.lastname@example.org now.
Login via email@example.com into central. Make sure all groups is selected in group selector. Then go to Maintenance > User management > add user. Add firstname.lastname@example.org.
Now register and then login via email@example.com and remove firstname.lastname@example.org :)