@Black-Cat Wow, thank you for all the information, that really sounds almost impossible.
I will definitely try to get some information regarding IEC 60669.
So if I got you right there will be one test report in the end which will cover all the different tests required by the different certifying authorities.
There are two things I still not understand.
Is it possible to certify a device so that it can be extended (through a defined interface) by self made hardware without loosing the certification?
What do you mean with the part about doing it myself? I think just not telling anybody would be difficult, as the assurance would like to know what caused the fire and therefore would do some research to find out. Or are you talking about the case when it is a Level 2 device and I only connect it myself?
I hope you understand what I mean. It's difficult for me to write down this part.