you can denature proteins, because their 3-dimensional structure is both complex & important for their function.
you can degrade or isomerize cannabinoids, but they don’t have enough complexity to their structure to “denature”.
http://chemistry.elmhurst.edu/vchembook/568denaturation.html
as for freezing cells rupturing them and making them leak, yep, it happens. if you’ve cured first, it’s less likely. If you’re after live resin, then getting it frozen fast, and not thawing, keeps some percentage of the cells from rupturing, and most of those ruptured cell contents out of your extraction. or so the theory goes…