I would suggest that you could say something like "appointing himself God." I have heard people say to one another "who died and made you God" or words to that effect and I think that this would go well with what Napoleon is doing in this book.
In the book, he really is setting himself up as something of a god. Everything he does is automatically right -- he is the perfect being. In addition, he is all-powerful. Anything that he says must be done. The other animals are supposed to look up to him. They are supposed to call him by titles just as people often call God by titles. Napoleon becomes like a god to the other animals.
So I think that, instead of saying that Napoleon is creating a leader myth and personality cult, you could say that he is "appointing himself God."