Antiviral medications like Zovirax, Valtrex and Famvir, lessen the chances that there will be a breakout but do not guarantee it. If a breakout does happen after laser resurfacing, it can involve the entire resurfaced area, so you must be very cautious about having such a resurfacing. In addition, no cosmetic procedures or any procedures for that matter should be done in the area of an active herpes breakout.
Medication pre treatment does not preclude the occurrence of an outbreak. It only helps to statistically decrease one.