BMW M-package retrofitting

Hello dear people from the forum, would be very nice if someone could tell me if one could sell a BMW as “with M-package”, even if the M-package was only retrofitted and not completely? My father bought a BMW 540i. Now we noticed that the M-package was only retrofitted because the blue or red M-brakes are missing. But in the advertisement was M-package. Can you do that as a salesman? Does anyone have experience with it? Greeting Paul