Re: Cannot change/set the resolution
Some observations from windows - it might help:
1. The game rewrites the CFG file at every exit (and creates a default one at game start if none exists), manually added entries will then be removed\overwritten. Setting the file to read-only is your only option unless you play a mod and add those entries to the mod's CFG file. I am not sure if you can adapt steam's custom launch option to start the default game with a custom CFG file as described here in the 'Alternative Launch Option' section. If possible it would allow you to use a copied and renamed CFG file with your custom entries.
2. If using windowed mode your game resolution has to be equal or larger then your desktop resolution to avoid an actual window.