It is very common for people (and vendors) to say that opening a device will void the warranty for that device. In the US, the 1975 Magnuson-Moss Warranty Act makes such voiding illegal. I just heard that mentioned in passing on the radio. Trying to track that down is proving a bit challenging to me, but it looks like 700.10(c) does it by prohibiting requiring repairs being performed by those authorized by the manufacturer. (Can't repair without opening, so...) Maybe it is more explicit in some other section.
https://www.ecfr.gov/current/title-1...ter-G/part-700
The FTC got serious about this with respect to electronics at least by 2018.
https://www.vice.com/en/article/gv5d...rs-are-illegal
https://www.vice.com/en/article/xw7b...do-ftc-letters
Of course, if any damage is done during or after the opening I assume the warranty is terminated.
I've created this thread as a convenience for reference for the next time the myth comes up on mobileread. If anyone has better references than the above please chime in.