Change a Google Apps username

First enable the Provisioning API for your Google Apps account.

Google Apps enable the Provisioning API

Download and extract Google Apps Manager (gam.exe).

Open a DOS box and get your domain info:

gam.exe info domain

Google Apps Manager gam.exe info domain

Change your Google Apps username by using the update parameter:

gam update user <olduser> username <newuser>

Google Apps Manager gam.exe update username 

As you can see in the screenshot above I didn’t got any information from gam.exe. But when signing in to my Google account was only possible with the new user. Thanks Google Apps Manager!

To clean things up, I disabled the Provisioning API again.