Active Directory Migration

We will be migrating all of our users from one domain to another.  Is there an easy way to update the existing users in AgilePoint with their new user names?  The User Name field is disabled when you go to Manage > Access Control > Users > Edit Profile.  Do I have to register the new user name as a new account?  If so, do I then have to manually go and add the new account to all the groups and manually duplicate permissions from the old account?

Thanks! :)
Laura