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?
This thread is way too old. But, now we can add more accounts. Its quite visible
I was searching of the same and came across this post. So sharing if someone else search for it
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.
Both the OpenID credentials are copied to the other SE account, when you click on the "Copy Meta Stack Overflow login credentials to all Stack Exchange accounts" button you find, for example, in https://meta.stackoverflow.com/users/162101/user162101?tab=accounts.