If you havent tried it and check the data logs I wouldnt say its not possible. I did the following upgrades with no problems what so ever. GTSpec Headers, GTSpec Uppipe, Fujitsubo Catback Exhaust RM01A, Invidia Downpipe, VF39, Forge Intercooler hose, Pony Express MIL Fix and a resistor for the EGT. Again I work at a Subaru dealership and the techs there are highly skilled. We even hooked up the Select Monitor(subaru scanner) and drove a few runs to make sure nothing is wrong. Car runs great and I plan to get ECUtek, modify my injectors, get a fuel pump, Electronic boost controller, and so defi gauges. My boss there says its even ok to run 16lbs of boost without engine management. ECU will compensate for the extra air unless you start messing with how many pounds your running. Mines running stock boost pressure.