Surgery on a bird is risky. All surgery on any animal is technically risky. Bad reactions to anesthesia, infections, too much loss of blood.... Many things can go wrong and mistakes can be made. That's if you paid a vet to do it under anesthestics which is going to cost you probably in the $100s per bird. Without anesthesia it's questionable if it's even humane (not surprising if it's illegal somewhere) and you'll have a much greater chance of losing the birds. In the end all the money or risk will get you nothing. When your guineas recover they will continue wandering just as far as before. You might have slightly less mating behavior towards other birds but if that's not an issue now you will have solved nothing. My guinea cock does have mating issues and seems set on breaking the roosters necks ever since breeding season started. I just locked him up for a couple days, clipped his toenails, and clipped one wing to hopefully chill him out and make him less capable of going after the roosters.