I no longer use the service that I originally used to register, and would like to change the service I use to log in, or at least add a second account.
Is this possible? How do I change my login provider or associate a backup method to log in?
For more information, see "How do I add or remove login credentials from my account?" in the Help Center.
Yes, this is documented on the Stack Overflow blog and in the Help Center.
You can add an unlimited number of logins of your choosing from the account page, by either going to meta.stackexchange.com/users/mylogins/current or by clicking "Settings" at the top of your profile → "Your Logins" at the left → "Add more logins...".
If this prompts you to log in as a different user, then you probably already used that "new" way to log in earlier. In that case see How can one link / merge / combine / associate two accounts / users? (Anonymous / unregistered / cookie, or Google / Facebook / registered).
You can also remove credentials you no longer wish to be tied to your account from this screen.
