I am going through a nasty separation which has escalated to the point of no communication. What steps EXACTLY do I take if I want to add my last name on my son's birth certificate. I am already listed as the father.

Are you wanting your son to have your last name? I am not sure what you are asking.

Hope this link explains all the steps

Adding father's name to birth record (http://www.health.state.mn.us/divs/chs/osr/rop.html)