I got conditionally approved for GE, though at my local airport the earliest I can get in for an interview is late October. If I schedule an interview then, can I later change it if i am traveling and I know I will be at another airport with earlier availability? Does space ever open up if people cancel?
Yes, you can change your appointment date, and, occasionally, appointment slots do open up but it is tough to know when that happens. The only way I know of is for you to keep checking by going to your GOES account and requesting to change to another slot. When I was approved for NEXUS, which uses the same procedure, I'd called to see if I could be alerted when a slot earlier than the one that I had selected opened up, but was told categorically that they could not do that...
Anyone want to give me odds that if I show up to the GE office in EWR tomorrow they will just take me in the morning as I connect?
I arrived about 30 minutes early for my appointment at SFO. They took me, no problem, but this was late morning on a weekday. Weekends may be more in demand.