Some libertarians are minarchist meaning as little government as possible, some are anarcho-capitalists. Pro-life minarchists would be fine having punishment of abortion be treated like any other killing of a human. Anarcho-capitalists would rather not have government have a monopoly on violence.
If the NAP could be easily dismissed by just reclassifying who is and isn’t a human, then yes some form of law setting clarifying what a human is would be necessary. You bring up THE most interesting debate though in libertarian circles IMHO. Tom Woods did an interview with Gerard Casey about this topic. I highly recommend listening to the interview and giving Casey’s book a read.