I believe that’s generally the case for hardware hacks. But I think if you flash custom firmware without opening it the certification would generally remain valid though. Or at minimal there would be no way for an insurance investigation to know.
The Chinese vs European marks are a particular point of confusion. But yes, could be fake too.
That’s the most common case with “Geegoo” branded smart devices. They can still be as good as intended, just missing certifications (and/or quality control). But the worst and most dangerous are fake devices trying to imitate some serious trusted brand devices with inferior/inexistent hardware. I ones bought solid state relay from well known brand. I received it and from visual inspection had expectation it was fake. I took it apart and found a circuit that was capable of switching maybe 5-10% of the power declared.