That's a good question. Do you want to preserve the warranty?
Often remove the cats from my motorcycle exhausts. They always spin up better and are much more fun to ride........never had an engine problem and remember some bike rev to 15,000 rpm plus,I still have two 200 cell catalytic converters instead of the four that McLaren provides. I'm don't know why there is such a big concern, everyone of my pass and current cars has had the exhaust systems changed. That said I have never had any warranty or mechanical issues due to this type of modification. I sense a lot of paranoia concerning something that should have no affect on the mechanical reliability of this car. Why would allowing the car to breath better create any mechanical concerns. All I can say is, I love it and have no regrets what so ever. Cheers....??