Can I obtain a protective order against my ex-wife’s live in boyfriend to keep my children safe from him?

My ex-wife’s live in boyfriend was currently arrested and charged with a domestic violence against his own biological teen daughter. The charges were reduced. On a separate offense, he was charged and found guilty of aggravated assault and spent 30 days in jail for this. This incident happened 8 months ago. I just found this information out. He was also arrested and found guilty (another incident) of destruction of commercial property. He had to pay restitution for this. I wouldn’t care who my ex-wife is involved with, however we have minor children in which they (my children) live with her in his home. My ex-wife has full physical custody of my children. This was best for my children at the time we divorced due to my career. Can I obtain a protective order on behalf of my minor children so he is not around them? Do I have the right to modify the custody agreement? I am not comfortable with my children living in a home with such an unstable individual.