It's one thing to not support the new engine when it has problems. It's another thing to destroy property that someone bought from you after the sale if they use it in a way you don't approve.
I understand it costs more to support an open platform. But it's a choice to support that open platform, and Motorola doesn't have to do that, they can hang up on Joe Average who did installs the mod just like a dealership would do so on anyone who screwed up putting a completely different engine in their brand new car.