If you began playing on a Guest account and choose to link a Call of Duty, Facebook, Line, Google Play, or Game Center account for the first time, the progress you made on the Guest account will automatically transfer to the linked account.
Your progress is tied to the original linked account you used. Progress will not carry over to another linked account of the same type if you choose to change logins.
Transferring Guest account progress to an account that is already linked is not supported. Also, transferring progress from one linkable account to another is not supported.