Fuel line pressure regulators are a thing you can buy. They come in different pressure ranges but most are adjustable within a set range, say, 4 to 9 psi, or maybe 1.5 to 5.5 psi.

Of course you would need a gauge on the discharge side of the regulator in order to set it correctly, but once set you could remove the gauge and install a plug in the gauge port.

These were all the rage during the late 70's when it was thought they would deliver better mpg. They didn't, but they did allow hot rodders to add a finer tune to their fuel delivery system.

I used one of these in the mid 70's on a large GM car from the late 60's and set it at 7 psi. The only improvement in mpg came from it acting like a fuel cut off when I stepped on the gas.