turbo-skylane,
You can have what you like on the roof(!) but it won't affect the way that the plane flies. The shape of the model itself has no effect whatever on the flying characteristics - these are defined in the flight dynamics files that tell FS what the plane looks like rather than the model. So you could design a model of a large house brick, but if you used the default 737 dynamics, then it would fly like the default 737.
(Which some might say flies like a house brick anyway!)
