Assigning shortcuts to special keys (ie. XF86 and more) =single key shortcuts

Hello everyone

I’ll try my luck here, and hope that my somewhat long question, has a viable fix.

I’ve recently succeeded in my age old quest of remapping the keys of my Razer Orbweaver, through ‘udev’ and ‘hwdb.d’.
(h/t: )

After some trial & error, I’ve remapped the keys of my Orbweaver to an assortment of different keys, that are not currently in use by my system.

These are mostly various XF86-keys ( ), and these (of course) do not show up in the shortcut selection menu in LibreOffice.

My plan was(/is) to use the keyboard as a shortcut board, (single key shortcuts) for various things in Calc, but now I realize (as I already knew, but had forgotten) that I cannot assign other keys to shortcuts, than the ones shown in Tools => Customize => Keyboard => Shortcut Keys

Is there a way of adding these keys to the list, or a way of choosing a special key for the various possible shortcuts.

I’m running Linux Mint 18.3 and LibreOffice (I’m not affront to upgrading both OS and LibreOffice but just haven’t seen the need just yet.)

EDIT 2020-05-03:

I see that someone mentions adding shortcut keys via API:

But I fail to find any mention anywhere else of how to go about that.
I guess I’ll keep looking and but now I’ve got something more to go on.

I’ve also seen ‘xdotool’ mentioned as a possibility (since I’m on Linux with X11 that’s a possibility) but it’s a more roundabout way, and offers more links in the chain that are able to breakdown, though ‘xdotool’ does look interesting.