Hey, I just finished making an ingame config editor. It is not a separate mod, but its when you go into mods on the title screen, and press the config button on a mod. If you would like to see my code, it is right over here, and to register that, add this line to your init function, in your CommonProxy file:

MinecraftForge.EVENT_BUS.register(new IngameConfigEventHandler());

You also need to add this to your @Mod annotation:

guiFactory = "refinedstorage.integration.ingameConfig.GuiFactoryIngameConfig"

done by @way2muchnoise in 5cfe092