Weren't all flights booked into/out of the NYC, BOS, and WAS areas (and several other airports around them, like RIC, etc.) allowed to be changed once, free of charge, under UA's weather policy for the weekend? This should apply to award travel as well; you can rebook for new dates if you want, or get a refund--though on the GATW certs, they might either deny a refund (and allow only changes), or maybe, just maybe, issue a new free flight voucher (or, depending on which call center, try recrediting your "miles" as if it was a normal award )

I moved my cheapo BOS trip that was to gain the last set of 10k bonus miles from UA's WAS promo to Tuesday without a problem (flights had to be by Wednesday, I believe, to qualify, and all-UA routings, or I'd have gotten those miles back in November). No charges, of course, and UA wanted to work with me to find dates & times that fit my schedule.