From Blogger Help: Login Troubles With the New Blogger
"Can I change my username in the new version of Blogger?
Currently you cannot change the Google Account associated with your account in the new version of Blogger 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."Well lah-de-dah.
Goodbye for a good long while.
And this time it's on purpose.