Some mods have custom config files that allow you to change how the mod behaves.
Config files will not be generated until the mod is loaded ingame at least once. If you just installed a new mod and need to configure it, start the game modded once!
Changing Mod Configs with r2modman
In the Config editor in your r2modman profile see all of your mods config files. Select the one you wish and click "Edit Config".
Once you have changed configs in your mod of choice be sure to press the "Save" button.
That's it! Now your mod should have the config changes next time you start the game.