Hi Janet B24,
My son, now 7, didn't express quite the level of dysregulation that you describe, but like you we sought help. He ended up being diagnosed with ASD 1, level 1 autism, what they used to call Asperger's before the DSM-5. How long has he been exhibiting these behaviors? Have you always noticed something a little "off" or was there a point when his behaviors or personality markedly changed?
We've kind of always had an issue with him hitting his little sister, 5 (unfortunately she's taken to copying this). Other issues are him head slapping himself, which I think it's a coping behavior due to anxiety.
I'm not a fan of reward charts. It seems gimmicky to me (take this as a personal bias). Mom used them in the other home, we're divorced. We did go through parenting classes last summer, 6 weeks each for both of the kids' age groups. They gave us reward charts to try. Seems like a low level first try. It may work for some kids.
I remember a couple having trouble with their son, and it seems similar to you. The first class, we heard the kid, 6, banging and yelling in the other room across the hall. His parents were at a loss. It went on for half an hour before it stopped.
The next five sessions, there wasn't a repeat. We were all blown away.
As best I can recollect, the therapists explained that they laid out the rules (boundaries) to the kids in the room. They kept the other kids safe, but let the one kid pound the walls and basically ignored him. When the kid saw he wasn't getting the reaction he was looking for, he eventually stopped trying.
I'm not trying to say that your son has autism, but ABA concepts may help. Truthfully, I've found the parent training portion lacking thus far, but I'll hopefully learn more. The supervisor pointed out that ABA is about human behavior, and the concepts can be applied to anyone (I was asking about D5).
The first step in solving a problem is to observe and measure it. They gave us something similar to this chart:

I finger-zoom on my tablet to see this. PC users can do Cntrl+middle mouse wheel up to zoom.
Original here:
https://i.pinimg.com/originals/f6/b5/3f/f6b53fa328f5089c6dd720222f7cd579.jpgI'd never thought of this, but it may be helpful to parents here with adult children with BPD... .keep in mind that ABA is most used for ASD, but I think logging or measuring behaviors and our reactions can be helpful. Antecedent--->Behavior--->Consequence.
Let me know if this seems helpful. I only can log in for long replies at night in my time zone, but I want to help in any way which I can. We can help support you delve into the communication tools which can help reduce conflict, too.
He's convinced he's a and person.
What did you mean to write here, that he thinks he's a different person?
I hope to hear more and how best weer can help

Turkish