I'm guessing no if you used EZAir and then paid United directly to upgrade. However, if Princess really needs your cabin, they may just work with you on that if United won't refund it to you directly. That would definitely be a question to ask in your response to the offer. By the way I've been able to successfully get United to refund the upgrade amounts that I've paid for flights that I cancelled (most recently in January). Technically United's answer is no to these refunds but I'm happy that they've been more generous than their written policy - and I hope it stays that way!