I know in QMK you can set up different layouts that you can switch to. This is used for switching between qwerty and dvorak and stuff like that. You could set up layers that have the space defined like you want it in each condition. Check out PDF(layer): https://docs.qmk.fm/feature_layers#switching-and-toggling-layers

The Planck keyboard default firmware does this on an ‘adjust’ layer: https://github.com/qmk/qmk_firmware/blob/master/keyboards/planck/rev7/keymaps/default/keymap.c

This is how I’d do it. But it’s not something that you control from the computer side. Also, having it baked into the firmware means you can use that feature on whatever system you might want to plug the keyboard into. I don’t know if that kind of thing is possible to set up with the VIA gui. But since you’re using arch (btw), learning QMK might be right up your alley!

There’s also this feature in QMK that I don’t quite understand called the ‘Programmable Button’ that lets the software interpret certain keycodes before handing off to the OS (I think that’s how it works? I might have that wrong): https://docs.qmk.fm/features/programmable_button

I hope that helps :)