Originally Posted by Billy Mumphrey

To answer your question directly, yes I have, but only in the situation of schedule changes or cancellations where I was eligible for a refund. To avoid losing the cert for a voluntary cancellation, I'd simply modify your itinerary to a future date (as far out as the calendar permits) where you find a comparable price. Then when you reschedule your trip just modify the itinerary again. This will be a lot easier for the agents than reopening the cert, if they even agree to do it.