that should be the build string, version string see [HOWTO] Give complete /e/OS version info easily for support, answers, comparison etc
adb sideload via wifi… I’d guess no, never tried. When the OS is fully booted, via adb root you can alter the filesystem to your liking. I was never a Magisk user, but I’m sure there is a guide out there explaining how to go from a shell with root permissions to what you want