It's hard for me to understand how one can maintain a delusion of grandeur by insisting he is Napoleon. How would such a person respond to the argument that (1) "Napoleon was a historical figure who died in 1821. If you are him, you must be dead. Are you dead?"
The delusion consists not so much in imagining oneself to be Napoleon but in the auxiliary false beliefs that accompany it, such as:
"I am the emperor of France."
"I command vast armies."
"I have been planning an invasion of Russia."
"All shall bow to me and acknowledge me as their ruler."
When a biological male imagines himself a woman, does he fall prey to a similar delusion? Here's why I think the analogy is less than perfect. For while both claims can be mistaken, a transsexual need not have the extra false beliefs like:
"I can bear children."
"I have a pussy."
"My breasts can produce milk."
"I am physically attractive."
And of course, it is impossible for anyone to be Napoleon; but it is possible for a person to be a woman; so (1) cannot be deployed against a trans person.
Hence a transgender person need not be considered insane like someone who "identifies" as Napoleon.