When I realised that it wasn't about trying to change him, but trying to change me, my life became much easier. Took me a long while to get to this point though.
I resented it hugely as HE had the problem not me... but once I became a bit more flexible - stopped sweating the small stuff and accepting that sometimes very little was the best they could do - life got easier.
For me it was reducing my expectations - accepting him where he was. NOT at all saying you accept the violence - but when I adjusted my thinking and started accepting that after school was horrendous for his anxiety, I found the meltdowns lessoned and the violence diminished. By expecting very little from him, he could calm down (lots of sensory strategies are good.) A snack he loved (so what if it was crisps or a sweet, why battle with a carrot if he was happier with something that I disapproved of!) If he needed to watch TV for an hour to wind down - so be it, rather than me sticking to my rigid ideas of how much screen time.
Not saying you give into everything - but when I'm stressed - I want wine and chocolate, not a glass of tap water and lovingly chopped carrots and healthy dip!
Before I would battle with him as I had my ideas of perfect and idyllic childhoods and was trying to hard to be a perfect mum. I was too concerned with what children should be doing after school, rather than what mine could manage. When I dropped trying to be a perfect mum - trying to do playdates / craft activites, limiting TV etc and started realising what my boy needed, (love, tv, snacks and space to just be) it reduced the pressure on him and the behaviour problems lessoned.
I sometimes feel I have sold my soul to the devil - All the ideas I had on good parenting have gone out of the window - but they were based on my expectations on having a NT child.
When I accepted that he wasn't NT and stopped worrying about what everyone else thinks and just went with what he needs, life became easier. I still sometimes feel bad that we should be doing more etc, but that is my problem not his.
We had some therapy and I was expecting them to tell me how to fix his behaviours and how to discipline him - what consequences to give etc. I felt really judged at first when they started telling me to change what I did - I'm not the one who bites, kicks, spits, hits. But when I got off my high horse, I realised it was good advice - when I chilled out about things - he chilled out. Still have the meltdowns at times of course - but have greatly reduced.
I accept that they let it all out at home - as they have to work so hard and contain so much when out. So at home I try and keep expectations to a minimum - we have rules and routines, but they are based on what he can do - where he is developmentally, not on what a NT child of his age can do.
It is so hard and at times relentless. I know it really hurts (both physically but more in your heart) when your child lashes out at you. Now I see it as a massive panic attack rather than naughtiness and it feels a little less personal.
I am very clear with a firm voice "No Hitting" etc if he is lashing out, as I think they need to know it is not acceptable behaviour. It has little impact though - if he is lashing out I try and remove myself , other kids and objects out of the way and offer sensory strategies (best before they are at full pelt.) to try and calm them.
Prevention is always better than cure, but you can't prevent everything. You can only do the best that you can do. Don't beat yourself up about it. Sometimes things change and you can't get in there to prevent it.
It does put so much pressure on you though to be constantly helping them to stay calm. It is really exhausting but remember you can only do your best. You are a mum, not wonder woman. it's ok to not get it right all the time.
Try and somehow get some time for you away from the pressure - I go for a run a couple of times a week, when my DH is home to look after them. I sometimes feel selfish doing it, as there are a million other things that I could be doing and mothers guilt kicks in (as I look at the ironing basket and the paperwork that needs sorting and the cupboards that need sorting out) and I feel selfish. But I need the break for my sanity. Not sure if you get any time to yourself but really try to put yourself first a couple of times a week.
Not sure if my rambling will help - I know at his worst I just wanted a magic wand to make him behave, but it 's just not so simple.
Take care of yourself.