Yeah they're good with exhaust modifications. You could also try talking to Scott at Hiflo Custom in Manassas. He owns the place and did the OEM perforated pipes mod on my M3 and he charged me next to nothing compared to the other shops in the area. His work is top notch too. But if you go to him be prepared because he's an a**hole at first but he's honestly a good guy and cares about his work.
M3 is gone. Pretending to be a dad now with an X5...