I believe your best solution would be to create a new WorldSettings class that derives from AWorldSettings - something like:
UCLASS(config = game, notplaceable)
class AMySpiffyGameWorldSettings : public AWorldSettings
{
GENERATED_BODY()
public:
AMySpiffyGameWorldSettings();
};
…etc. In the constructor, you can override whatever default values you’d like, add new members, override functions - anything you need.
Specify the worldsettings class to use in your DefaultEngine.ini:
[/Script/Engine.Engine]
WorldSettingsClassName=/Script/MySpiffyGame.MySpiffyGameWorldSettings