My old Google account was overtaken by spam, and so I'm transitioning to a new Google account.
Is there a way to migrate my Stack Overflow identity to the new Google ID?
In your user profile, close to "edit," there is the "add openid" link; using that link you can add another OpenID account (in your case, the new Google account). If you have already defined two OpenID accounts, the link I reported becomes "change openid;" using that link you change the alternative account you already defined.
You can also swap the main OpenID account, and the alternate account.