It would be quite handy to have a way to set this at runtime via command-line arguments or environment variable without having to edit an INI file for scripting purposes, especially in Linux.
EDIT: looks like adding r.GraphicsAdapter=2 to CarlaUE4/Saved/Config/LinuxNoEditor/Engine.ini has no impact, CARLA (UE4 powered) is still running on GPU 0 on my Ubuntu 16.04 machine
EDIT 2: Other users are reporting the r.GraphicsAdapter setting not working, tried it in ConsoleVariables.ini as well.