I'm fairly sure exhaust shouldn't need changing for RWC. Always thought it's fine as long it's secured properly and EGT sensor attached, and exhaust noise is EPA related or RW/Vicroads like to screw us lot?
That brings me to a story; Last December i bought a 32 GTR, seller said he had to put stock exhaust in cos the Apexi N1 is too loud to pass RWC, That being said, the system consists of 3" Y pipe, de-cat and stock catback. He then swapped back before I got the car.