Groundhog Day #1: AMS hits an awful lot of people about Trail Camp. Better preparation is to spend two nights at altitude before heading up the trail.

Groundhog Day #2: You can pretty easily just walk into the Visitor Center where you picked up your permit, and ask for a No-show permit. Google Unused Whitney Permits. Also look at the Wilderness Permit Options (link on the left) for more info on walk-ins (see box 6 in the WPO).