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