It is a passive forced induction hood, meaning it works when the car is moving.
There are other styles of hoods that offer a passive induction, such as a cowl induction hood and the reverse teardrop (not as good as cowl induction).
Yes, you could use other systems, see if you can find a parts man at Ford to look up the part numbers for the extra intake systems for the police version, or find a wrecked police car in the salvage yard and get the cool ram air system off of it. It might not be as impressive to look at, but it will work better then most aftermarket set-ups.
A shaker hood is a type of air induction system where the hood scoop is attached to the carburetor/engine and protrudes through an opening in the hood. Therefore, the scoop "shakes" with the engine vibration, but the hood remains stationary because the two are separate pieces.
It is an air scoop connected to the engine, not the hood.
But "Shaker" is a registered trademark of Chrysler Corp used in the late'60's -early '70's.
For every 10 degrees drop in ambient temperature you get 1% increase in HP.