Not the pad lock on the coop, but the gates around the yard. Temperatures generally only gets down to the mid-20's at the coldest here. I suspect this technique would not work below 0F. But, y pad locks seize probably due to frozen condensation on both the pins in the keyhole and on the hook. I get them open by holding the lock in my fist in one hand and jiggling the key in, then jiggling the key some more until the lock pops open. Basically, use body heat on warming the lock and body heat transferred from key to inside lock loosens everything up.
If you are talking below 0F, I probably would not try this due to risk of hand injury. Metal will carry heat away very fast.