2014 and this still isn't a feature. Unreal. Unable to change an email address in 2014.
Bravo Atlassian. What's your excuse? It's too hard? It's so hard to have a user table with a primary key of ID that is a sequentially generated number and an email column that can be updated.
If your data model actually has the email address as the primary key then your DBA / devs need to be replaced.