I was wondering if it would be safe to chill in the fridge--or even freeze in the freezer before giving it to the dog. My guess is that it would either make it brittle and unsafe, or it would become a nice chilly treat for puppy teeth.
If you have decided that feeding rawhide to your dog is appropriate, I don't see why freezing them would be any cause for concern. Many dogs enjoy frozen treats.
There are a couple of lines of thought on if rawhide should be feed to a dog at all, these are addressed in our existing question Are rawhide bones or natural raw bones potentially dangerous for a dog?
I looked around for reference for or against, offering frozen rawhide treats to dogs. I did not find anything different then offering them unfrozen. Frozen hide/leather does not get brittle.