In past years, there has been a 72-hour cancellation policy for Food & Wine Festival event bookings. I assume it will be the same this year.
A few years ago, when I tried to change a booking for four into a booking for two, I was told that I would have to cancel the entire reservation and then rebook but that there was no way to prevent someone else from get the slots during the time between canceling and rebooking.
If you're going with another couple, and that couple might need to cancel, I would recommend making two separate bookings. Also, your credit card will be charged immediately (actually within a day or two). So, unless you're planning to treat the other couple, you may want to ask that couple to book using their own credit card,