At the worst, you may have to call Comcast and have them clear the PIN's, which may require a hard reset of the box, clearing everything such as reminders and iGuide personalization. If it's a DVR, it could erase any recordings and scheduled recordings.
wow..it DOES PAY to read customer comments....having same issue with the on demand requiring a pin number and DID NOT want to spend time holding with comcast either.::...so THANKS to whoever figured it out...will try it!!