So the game starts with a dialog which lets you rebind inputs.

That does nothing.

Modding guide says you can create keyboard layouts, but export in libreoffice doesn't seem to work and in any case I don't really want to create a new layout, I just want to rebind the movement keys...

I tried taking the controls_qwerty.json, changing the keys in there, and sticking it under game/Mods/mymod/ but game doesn't seem to pick it up.. strace shows it's not even trying to open the file.

How hard can it be? :\

EDIT: you can find the hardcoded bindings in game/Epistory_Data/resources.assets and just overwrite them. Look for controls_qwerty. You probably have to stick to bindings that do not change the size of the file since it's binary and might contain fixed offsets.