Originally Posted by
shady
Yes, you can modify your existing reservation. You just do a new search after you click modify, adding your code and continue just like regular reservation.
Sometimes though Hertz.com won't apply the new coupon properly to an existing reservation, so you might want to try a fresh booking first just to get a baseline price before trying to mod your existing one.
One little trick is that if a coupon will not apply when modifying, change the car type to get Hertz.com to reset and apply it. After booking with the new car type, you can then go in and modify it again to go back to your original car type.