hrubago

I booked car (next month i will buy it) STi 3. The man said that the car was optimized by Power Engineering... The car has PE Exhaust manifold, downpipe, Blitz intake etc..... Now (308 hp) but on low boost(he said..). Is possible to try increase turbo pressure now? (maybe HKS EVC-R will helps) or its impossible to run on two different modes (smaller and higher pressure then PE setup?) Can i do myself or I must contact PE? Are the fuel maps from PE usefull on diferrent turbo pressure? How much PSI i can add?