Well, what exacly do you want to achive?
As far as I know you can only enable or disable reprojection in the Steam VR Settings under Performance Tab.
But I don’t recommend disabling it since you will get black frames if your Application is not running at 90 FPS constantly.
There is no such thing as 80,70,60,50 FPS, only 90 is stable (44 kinda is, but it feels really slow.)