I've only had a few boars castrated, but I really feel they have changed after the op. Now that could be because they have then been put in with sows and that in itself has changed their behaviour. Eric, in particular, was a very fiesty little man, but after he had been castrated and became part of a group with three sows he became very submissive. In fact for a while I was worried they were bullying him, but he seems happy enough but without doubt he is bottom of the hierachy.
I guess if anyone has boars castrated in the hope they will then get on better together, and it doesn't work, then they have the option of getting them each a girlfriend.