Actually, guest relations can not reset your biometrics. Anything that has to do with biometrics is all done at the turnstiles. If your biometrics don't work, after you show your ID, we are supposed to reset it. The only peoblem is, if we reset it, it uses the reading it just got (the one that didn't work). So if you don't do it like that, it won't work again.
Biometrics can be a bit of a hassle, but it's the best method Disney can find for a quick ID check. It's that or checking photo IDs manually and that takes a LONG time ... especially when you have a huge line at the gates. Believe me, this has happened. Your best bet is to always carry a photo ID and you will never have a problem.
Nick