Dude, Mazda makes a CAI, CBE, fully adjustable coilovers, rear camber links, lightweight track wheels, and more for the MS3. Aren't these a form of OEM equipment? Why can't other companies make products with similar specifications as these parts? Isn't this what MM was made to protect consumers from? Are these not used to extract more power/faster track times from this car? Mazdaspeed will also sponsor cars that compete in more than a certain number of events per year.
Not all of those parts are warrantied. The coilovers, for example, are covered by an Orange warranty (off-road use only) in which you assume all liabilities.
Mazda is not as quick as you might think to void warranties (true story). They rely heavily on dealer input. Most techs are not stupid... they can tell when a car has been abused or heavily modded (even if you remove all parts). If you mod with a part without a Green or Blue warranty, you are indirectly at risk. It is not hard to connect an aftermarket part to a failure.
This whole rumor about using outside sources to void Mazda warranties is false to a point. For larger repair claims, Dealers go through a quick approval process to have the work reimbursed. Warranty work is easy money for the dealer; they WANT to do it. However, if the dealer or Mazda Regional Rep suspects foul play, they "might" do a bit of investigation. Or, if a dealer/region has a higher than normal claim frequency, it may be given some extra attention from Mazda NA. That's about it.
We've all heard of innocent owners being given the run-around on a stock Speed3 or Speed6. They are VERY limited and happen usually because of the following:
1. Someone can't provide evidence they completed required maintenance at the correct interval.
2. The dealer falsly diagnoses the issue as owner negligence.