[yetibone]

You would have to decrease fuel delivery from the injection pump to decrease power output. I've seen fuel delivery increased before to raise the output on road, and farm tractors, or when turbocharging is added, but not the other way around.

I would guess that the power units are certified for their respective outputs at the crankshaft by the manufacturer. Turning down the fuel rate would decrease the power, but the air quality police would likely still have to regulate based on the factory's standards for fuel rate on that power unit, and not on an altered, and non-certified fuel rate.