Any way to "de-power" a power steering box?

If you want manual steering, convert your car properly to it.
Don't fool around with taking the belt off etc. on power steering because it's brutally unsafe.
If you get into an accident with the car and they discover the car is modified to defeat the power steering, you'll be going to jail or fined. (Or both!)
You might as well defeat the front brakes as well while you are at it, the car will still stop using the rear brakes, so why not remove the front brakes? Think of the weight you'll save!
DON'T DO IT!