I was thinking of writing one of the premium dog food companies to see wht they said but did a google and a previous Yorkietalk thread came up:
http://www.yorkietalk.com/forums/842851-post14.html It is a pretty detailed response from Innova. Makes sense!
Although they don't recommend freezing, they only mention palatability as the issue. If your dog is liking and eating it after freezing, then that would seem not to be an issue.