Welcome to Yorkie Talk. Mr Willie is adorable, and almost looks like a little statue in that pose
I am surprised that he isn't overweight, eating cat food. I've heard that it is too high in fat and protein for dogs (but may be mistaken). Anyway, good that you are getting him on an appropriate food for a dog, and hope he will accept the change. It will be like taking a kid off a diet of candy and getting them to eat real food.