Is it possible to set a global key combination in linux like alt+sysrq, but with its own command/script?

Question

linux

Is it possible somewhere to set a keyboard shortcut in linux as Alt+SysRq+<> to work absolutely everywhere and hang your own script/command on it?
It should not matter if the user is logged in or not, if Xorg is running or not.
Not necessarily Alt + SysRq + <something> - this is just an example.
Preferably without rebuilding the kernel.

Answer 1

/etc/inittab