I want to legally not have any association with my adult child who I don't want any legally or moral responsibility to or for him to be legally to any estate of mine in case of my passing. He is a drug addict and is nothing but a total nightmare who is physically and mentally abusive. I want to sever all legal connections

You have no legal responsibility for an adult child.
Moral responsibility is not anyone's concern but your own.
Your will should mention a child you want to not inherit, so that the child cannot claim that you 'forgot' in a clouded mental state. A lawyer can help with the wording.

As noted, the only issue is your estate. Some areas do not permit a complete disinheritance of a child. So you NEED to consult an estate attorney to prepare a will properly that eliminates any claim he might have on your estate.

And no, you absolutely cannot change the adult child's name.