I bought a new Windows laptop recently and immediately disabled Secure Boot and installed Linux. Today, a screw fell out of the laptop. Obviously, installing Linux had absolutely nothing to do with this. Could the company refuse warranty service because I installed Linux? Of course they can't if the agreement says they can't, but if it says they can, is there any law (e.g. Magnuson-Moss Warranty Act) that would override the agreement?
In the USA the Magnuson-Moss Warranty Act of 1975 defines the rights consumers have with respect to product warranties.
In your case the change you made would have to have a direct cause-and-effect relationship to the problem for that specific claim to be denied. For example if you installed a non-supported hardware item and it pulled excess power which damaged the power supply, the manufacturer may be able to deny the claim due to your use of an incompatible accessory.
The idea that installing Linux has any relationship to a case issue (i.e. the screw) is pretty far-fetched so there should be no question that the change is totally unrelated to the problem.
The law supersedes any language in a specific product warranty agreement that tries to circumvent it. The FTC recently warned some manufacturers, including Harley-Davidson, for violations of the Act. Note: