You can increase the internal pump pressure which ends up knocking pressure inside the pump up and therefore output to an extent if you want too...but you have to be careful with it...
It involves using a punch and a light hammer and "tapping" the pressure relief valve (look where the pump fuel inlet is...now "in back" of that, more towards the engine, looks like an "squared oval with a circle in the center, countersunk in" usually marked from the factory with yellow paint.
Insert the punch...a tap that center portion just a little...ever so slightly (you should see it move and leave a slight mark from where it "used" to be and where it will be) and internal pressure is increased... some have seen a little bit of gain off this...others, a bit less noise...but TRIED AT YOUR OWN RISK. If you tap it TOO far... the collar that retains the valve will plop down into your pump and the only way to get it out is to remove the valve, fish out the collar, diassemble the valve, tap it back up through and start over
There is some info on it over at TDI club if your interested...maybe on here as well, but not that I've seen in any threads.
And...this is not to be confused with the "Hammer Mod" used on eTDI pumps
Joe