Crowing, mounting, and aggression is testosterone driven. Take the testosterone away and those behaviors go away. Crowing might still happen if done on a roo that has already 'found his voice' but it's not a full blown crow. I have one capon that crows but it's a weak and short crow. My d'uccle roo went from a feisty sound machine to a silent and calm flock member. It took 2 months for his testosterone to leave his body and him to stop crowing completely.
So how would one go about learning how to do this? I'm not sure its something I want to do right now but I would love to learn how.