Mods and warranty
Basically, according to the law, any warranty has to be honored unless they can prove that your modification is reasonably responsible for the damage.
I was told that the SL55 Intake will not void the warranty. It's a MB piece and doesn't really interfere with the original design/spec of the motor.
As for exhaust - everything I'm reading says you won't get any power gains as the exhaust on the C32 is just about as efficient as you can get. If you just want more noise, go crazy.
Pulley kit - I'd guess this will void the warranty (at least when it comes to any engine issues). Increasing the boost pressure to that outside the original spec can cause failure of certain systems. There are some cool dealers out there who will work with mods, but if you have a big engine problem and a pulley kit, I don't think even the coolest one will still warranty the repairs.
There are also unfriendly dealers out there who have refused to replace faulty bushings because an owner had aftermarket springs on the car.
YMMV




