Will Holy water applied topically have beneficial health or protective effects?

This will if it is believed that it will happen by the person receiving the anointment. This is a divine signal—the ritual requesting divine assistance for whatever is the intention of the anointment. It can be a simple blessing which is vague and non-specific as to the desired consequences other than a feel-good moment when the person believes they are doing something sacred and attending to necessary ritual to please God and show their obedience—that is a weak intention with regard to the prospects for betterment of the person. After all, they are already in good standing with the divine and need no demonstration of diminishment in order to be accepted as not being greedy or selfish in some way wanting assistance. It is very much the case that such a stance will get in the way of receiving divine help altogether because it is making the decision of being unworthy and the divine realm must stand aside under these conditions. There would be no difference between anointment on the skin versus ingestion of Holy water and its potential effects on the body. It is the intention of the ritual—who provides the water, and what the provider, as well as the recipient, bring to the overall intention of the ritual in terms of their belief quotient in the divine, as well as the worthiness to receive divine grace and, in addition, the self-acceptance by the recipient to feel divine assistance is possible and likely. So in this respect, the magic is not in the water, the magic is in the intention for there to be a partnership with the divine through this symbolic anointing of a person with water carrying this blessing.