The unsubscribe is for all messages from the expiry bot, for all certificates. It isn't possible to unsubscribe for just one certificate's expiry warnings.
Yes, unfortunately changing your ACME account email is still the only way to resubscribe.
Hope that helps! I know this isn't the most convenient experience.
I would definitely recommend that you monitor your own certificates for expiry in addition to relying on the expiration warning emails from Let's Encrypt.