The decrowing surgery is done on the syrinx. It has a 50/50 chance of killing the bird because that is part of the respiratory system. That is the biggest reason for not doing it. Those who have roosters that it's been done on have said that the boy will still try and crow, but it comes out as a raspy whisper.
Caponization has to be done when they are very young and there should be no testes growing back. They aren't like the liver that regenerates itself.
If you look around the site here or the internet you can find instructions on how to caponize. The tools are cheap. It's very easy to do it wrong when you first are learning. No anesthetic is used because of the danger. It used to be used to get larger table birds that weren't tough.
Some kid had a few year old capon at a show I went to that they used for their showmanship bird. Was the biggest, friendliest baby. The capon didn't have all the big rooster hackles, saddle, and tail. It was more muted like you'd see in an immature juvenile.
Of note is that if a hen's ovary is damaged, the hen will start growing in rooster plumage and acting like one. She won't produce sperm, though. Hen's only have one functional ovary. Nature is weird.