Have you spoken to any families with experience with the hospital you'll be using? What are their experiences with refusing standard procedures?
You have every right to refuse the eye ointment, and should be clear about that, but I think you're not accomplishing anything with the line about battery.
I'd go with something like:
"Mother (name) has tested negative for chlamydia and gonorrhea, and will be having a c-section. In these circumstances, erithromycin eye ointment is not medically necessary, and we are formally refusing it. Should these circumstances change, we prefer to decline the eye ointment unless there is a specific medical concern, and we require you to obtain our consent before administering erithromycin."