Whilst outside of using Cheats, changing the scale of the game isn't possible, by using the command
v_forced_aspect_ratio you can make small adjustments and tweak the scale of your game.
For example, from my HWR.exe.cfg file, I have the settings:
v_resolution 1920x800 v_fullscreen 0 v_vsync false v_forced_aspect_ratio 2.400000
This means I've got the game set to windowed, the aspect ratio set to 2.4, and the resolution set to 1920*800 (which I'm guessing is 1920x1080 with a 2.4 aspect ratio, as it gets rid of the bars in windowed mode)
Whatever resolution you're playing at, try using the command
forced_aspect_ratio X in the console, putting in numbers for X, pick something like 1.5, and work your way up til the game goes to the next resolution scale down.
See below for pictures that give an idea of various scales at set resolutions. The black bars are a result of the aspect ratio changes, and in full screen view cannot be avoided.
When you've found an aspect ratio you like, you can use
save_curr forced_aspect_ratio in the console to save it to your config.