No. If you look in the throttle body, air flow is controlled by a blade which moves when you depress the gas pedal. Even if you were able to port the extremely thin metal of TB, the blade would be too small for the enlarged opening and you would not be able to idle correctly as air would flow around the normally closed blade.
You can over bore the stock throttle body but you will need a new throttle plate. It is just a stamped piece of brass with a beveled edge. The problem is that it will probably cost you like 150 bucks for the job and you are not going to be able to go close to as big as after market TBs. You would likely have a taper bore which is not really ideal for air flow considering the size of most mustang intakes.