In an answer of my question on Code Review:
I am pointed to the right solution for this problem, that being a command:
setxkbmap -option numpad:mac
which proves to work when I invoke it from logged in session.
I am trying to invoke it on each reboot / re-login.
So far, my best guess was to edit my user's
$ crontab -l @reboot /usr/bin/setxkbmap -option numpad:mac
But this does not seem to work for some reason.
Just to note that this is not a duplicate of questions formulated like How to keep NumLock always on.
I have now tried to add a little (from terminal working shell script) to Startup Applications to no avail: