I was on the BMW website and I couldn't tell if they have any engine, exhaust, suspension mods for newer Z4's. Does any one know of any "tweeking" I could have done without voiding the warranty.
As a general rule any 'tweaking' will invalidate the warranty on at least that part of the car.
Since it's a new model and you appear to be looking at BMW options why not call the dealer and see what they have available and get their 'US' opinion on changes.