Does CFM of a compressor increase if pressure is reduced?
Absolutely Yes, this is simple physics the air is not requiring as high of pressure the throughout increases. Most air compressors rate there pump rates around 50 psi, 90 psi and the max psi. Even my cheap little pancake oil less has a dual rating of 3/6 scfm I don’t know for sure the exact number but was able to find the formula on line.  Just Google the ideal gas laws and there are many examples of this formula.
PxV = nRT ;
where P = pressure , V = Volume, T = Temperature, n is the amount of gas present
and R is a constant depending on the units used for the other variables.
There is a practical limit my 5000 psi compressor is only rated at 6scfm the volume increases as I reduce the pressure but because of the volume of the pistons and motor speed it will not jump as high as my little pancake compressor.