Selecting Dark Vision on the hotbar everytime I want to enable/disable it is pretty annoying. Is it possible to bind a key to toggle this power, e.g. by editing one of the ini file?
Since Dishonored is an Unreal 3 engine based game, you can try setting up an alias which will chain two commands: switch to a particular skill (or at least press a specific number key), attack.
See the ue3 docs: ("key bind chaining" & "key bind aliasing")
You can probably derive the commands for left-hand/right-hand attack and skill selection from the INI file(s). At the very least you'd be able to automate the 1-9 selection and attack, and then fill the slots manually.