The situation does raise interesting questions.
Let's say a female model on the books of an agency transitions to be a transman. A client requests a female model. If the agency asks the transman to go along, that would offend the model's new identity and quite possibly would piss off the client.
Another client requests a male model. If the agency sends the transman, that would please the model in terms of validating their identity but would most likely piss off the client.
The solution from the model's point of view is that when requests for male models come in from clients, it's the agency's responsibility to persuade the clients that what would suit them better would instead be to use the female model identifying as a man. But this would be a nightmare for the agency.
Basically, there has to come a point when a trans person becomes responsible for the consequences of their transition in terms with how the world perceives them. It isn't for the whole of reality to bend around the self-perception of the trans person.