Genetic engineering-the development and application of scientific methods, procedures, and technologies that permit ***direct manipulation*** of genetic material in order to alter the hereditary traits of a cell, organism, or population.
I have never heard of someone manipulating DNA for antler traits.
Yes people selectively breed for antler traits like mass, tine length, look, width. What farmer doesn't breed for phenotypical traits? Not everyone breeds for total inches or they would all be Frankendeer(not my kind of animal).They are going to grow bigger antlers when they are farm raised because they are not parasitized, are vaccinated, treated for sickness and they eat better than any wild deer has the ability to. In the very near future there will be a live test for CWD and a vaccine.