[eelnoraa]

I think the keys are “related”, and bmw has to give valid justification for the denial.

A positive case example can be if you mod is to increase redline. And for whatever reason, your specific engine has lower tolerance than average, and this mod creates a piston to valve contact, then bmw will sure deny engine warranty. But they cannot deny a warranty on unrelated components such as, say a cooling like component thermostat.

The concern is really not the mod will cause issue for general population. It is about if that component is outliner to begin with, and maybe the related mod pushes over the edge, then warranty claim become difficult. Chances are low, but non zero.