With sado-masochism legal would it be correctly categorized as an example of a lawful practice that involves intentional harm to self or another? Yes. I believe that would be a correct categorization of legal sado-masochism, similar to a situation in which pit bull fights are legal, the difference being that it is inevitable that one of the pit bull's ends up dead or severely mangled whereas the sado-masochists sometimes live to desecrate each other or other people another day. If it is not legal for dogs and chickens to be in situations where they are subject to intentional harm, why should it be legal for humans to be in similar situations? Cops hate being called to out on domestic violence complaints. I bet they hate it even worse when a neighbor calls them when hearing sado-masochism going on.
No, there are not examples of lawful practices involving intentional harm to oneself and another, because hurting oneself hurts society. A person who hurts themselves will have bills for medical treatment, and also for mental health treatment. This costs society as a whole. People who hurt emotionally should find other ways to express their pain than hurting themselves.