lame.

Can I change my Blogger in beta username?
Currently you cannot change the Google Account associated with your Blogger in beta account if you use a Gmail email address as your username. It currently isn't possible to change your Gmail account username after you've registered.

If you're using a Google Account registered to non-Gmail address, you can change your account email address. To do so, please visit the Google Accounts page and sign in to your account. On the next page, you'll be offered the option to change your Google Account username.