I m working on a VR experience where the player can look around in a creepy room and get his head chopped off at this point i want to disable the rotation to make it a better experience because dead people cant look around. i m working most with matinees, cameras and BPs. Is there a way to toggle that? Like in roborecall
if i were you, i would try to think what bothers me to come to my solution… if its your camera you could DISABLE LOCK TO HMD, if you run your camera rotation through other calcs, make A BOOL SWITCH 
just to add, IF your character is about to get up(not in this decapicitated situtation though :-p , etc. if he gets a knock hit and you want to play fall animation) because am also doing it this way, try to get your final rotation from the anim, and the moment your character gets up and should enable HMD controls, reset YAW orienation with the give YAW from last animation.
I think you can also set the position in the tick without setting the rotation, this will overwrite the default camera behavior.
