Will teachers lower expectations
Not in my experience, but teachers will be alert to potential problems and they will be less likely to assume that he’s just being rude/bossy/naughty. (Well there are probably exceptions, but then there are always occasional aresholes in life! One of my friends' kids has been bullied by a teacher, no SN involved. My DS has not.)
or treat him any different?
Yes. For example my DS’s teachers simply tell him when he has said something inappropriate. They rarely get angry and scold or punish, as they might if they didn’t know that he doesn’t always understand what’s appropriate.
My DS was given a lot of support at primary school. He needs (and gets) much less now. At secondary he asked not to not have a teaching assistant nearby; the school were happy to try withdrawing that support, and he was fine without. As he’s grown older he makes more of his own decisions. When he is 18 it will be his decision to disclose his diagnosis, or not. And other people will not have the right to pass it on without his agreement. He is high sets academically and the school expect him to go to university.
Social demands increase as children get older; but at the same time children mature. So things can either get better or worse as your DS grows up and that can change up and down - if his social development gets out of step with the other kids he might have problems again. And it can be harder for a teenager who is starting to get self conscious to accept help that’s being offered or accept a diagnosis than for a younger child.
Good luck. We had no choice about getting assessment done because DS was obviously not coping at all; it's not an easy decision when you have a child who seems to be coping 