the fuel pump is driven off the camshaft.
It is indeed true that earlier GTI's had the revision A camshaft which is soft, leading the lobe to wear , which in turn reduces the ability of the pump to supply fuel (ergo owners see fuel cuts as the first idea somethings wrong, usually when mapping/with hpfp). I doubt thats your issue though (but worth checking)
I am however shocked about the response from SC.
Even the slightest indication you have a rev A and are having issues then you need to get it checked. pump off, and check the cam follower / lobe for wear, not turn down the map!
buy a new follower and change it while the pump is off
VW may even warranty it if its worn. (if you put the std internal back in)
from what little I know the actuator is not something you go playing with without knowing what you are doing, I would only ever entrust this to a tfsi specialist (e.g JKM) who can log the car fully to ensure its set correctly. Its not something to my mind you just 'tweak'
as others have intimated, Id suggest getting the car healthchecked (cam follower etc) , flash car back to stock,reset the handset and sell it, then move on to REVO/GIAC/APR
(for the K03 I'd suggest REVO imho)