The definition of a "Free Night Award" is either a points redemption or another program benefit such as the Cat 1-4 or Cat 1-7 awards.
You can apply GoH to an existing reservation.
However neither the system nor the agent allow me to add or make a new booking stacking with C4 and GOH award. They kept saying the "free night award" means points redemption only. I escalated to the supervisor and solutions team but they don't budge at all.