Roosterred has a thread about rooster control. I do not think you can make him nice again, but you can make him respectful. Sadly, a roosters job is to defend, and he thinks thats what he is doing. I had the very same problem with a sebright cockerel. He may not like one person or be sensitive to a certain color, or think everyone is a threat. What worked for me was taking a narrow stick (like a bamboo plant prop) and whacking him on the neck a few times when he tried to jump or use his spurs. Not to knock his head off, but to immitate a sharp peck from an alpa bird. You must be consistent and persistent. It may take a few times but he will get the message. I hope this is not a typical modern thing. I was planning on getting a pair of bantam moderns!
Good luck!