With UE 4.25, the UE_GAMEUSERSETTINGS_VERSION value is here: \Engine\Source\Runtime\Engine\Private\GameUserSettings.cpp
Unfortunately, this doesn’t seem to be working properly for me. It works if I ‘Launch’ the game from within the Editor. However, for packaged games, the values seem to be ignored. I would appreciate any suggestions!
EDIT: Turns out this was user error, but in case it helps somebody else: make sure you delete your GameUserSettings.ini file from the application data directory if you want any changes you make to DefaultGameUserSettings.ini to show up. Once you run your application with a DefaultGameUserSettings.ini, those values will be copied to GameUserSettings.ini and override any updated or new ‘defaults’. I believe the typical directory would be %LocalAppData%\[Project Name]\Saved\Config\WindowsNoEditor\.