Do you just want to change the value of site settings? Just do SiteSetting.whatever='new value. Or do you want to change something about them?
Don’t you just want to add a setting for that? Just add to config/settings.yml? something like
If that’s what you want, then using rake plugin:create[plugin-name] will create the settings file for you, complete with example.
Or maybe I don’t understand your question.