I would like to run 1920X1200 HiDPI on a my 13" MBP Retina.
Before upgrading to High Sierra I was able to do that either by manually adding the 3840x2400 resolution by following the tutorial in the link below. But the /System/Library/Displays/Overrides/ folder does not seem to be present on High Sierra:
As an alternativ to the manual method above I could add it SwitchResX in the "Custom Resolutions"-section. But when I add the resolution it just says "Not installed".