actually...because airfoiled stabs are airfoiled, and not flat, their efficiency creates far greater control response than flat surfaces. so they do make a significant different difference in handling. (try a knife edge loop with a flat stab rudder, it gets pretty exciting towards the end!) some airplanes have gone through design iterations that went from flat surfaces to airfoiled surfaces, (original Aerworks Edge 540 comes to mind) and that singular change resulted in an airplane with far greater tail authority for both precision and 3D. but getting back to the question....replacing flat stabs with built up stabs can be done, (on some airplanes) but it is a lot of work, and requires a pretty good understanding of how it is done on larger airplanes. good luck.

Paul