In debian based systems, there is a command that fetches the source code to any package (including the kernel) called apt-source. You can run that to have a cop

In debian based systems, there is a command that fetches the source code to any package (including the kernel) called apt-source. You can run that to have a copy of the source used to build whatever package you are in. Then you make your changes, and run another command to build packages from that source (.deb files). I have occasionally made use of this to fix my own bugs. One time, an old thinkpad started shutting down unexpectedly due to a bad thermistor reading. I was able, in a few hours, to patch the kernel to ignore it, thus extending the life of my laptop for years beyond would have been possible in windows. The benefit of ability to edit your own source code is real. Maybe rarely needed in practice, but linux is all about the long tail.