When I had my interview for GE, I specifically asked whether I had to schedule an appt. when I got my new passport, the answer was NO--just come in.
I'll find out in a few days when I bring in my new passport.
I was told the same thing. The other thing I was told was to be sure to bring your enrollment number/letter to speed things along. The scanning and stickering surely takes about 1 minute once they locate your account.