Even though I disagree with the notion of software changes nullifying a hardware warranty, that is a cute way to do it that I’ve never seen before.
Any design worth its salt should incorporate a thermal soft-fuse at the heater element that cuts power off if the printhead ever goes above the maximum temperature that any filament can handle.
Pure software interlocks are not sufficient. One might think people would have learned a lesson, nearly half a decade after Therac-25.
Loading untrusted firmware onto a PCB with high current outputs - like motor control - should absolutely void your warranty (for that PCB and anything connected downstream of it).