i would advise anyone wanting to modify these root level files to make a backup before starting in, such as:
cp /usr/share/X11/xkb/symbols/keypad /usr/share/X11/xkb/symbols/keypad-bak
esp when it comes to the main layout for your language like /usr/share/X11/xkb/symbols/us
because a misplaced character or missing paren can render you unable to even type in a password at the tty screen.
that’s when you boot to grub (or a live USB) and rename the backup file to restore the defaults.
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i would also suggest that it’s better to make a new variant, rather than tinker with the core definitions.
then you can just paste in an entire section that you can keep in a text file like i’ve one for my custom symbols layout