Instead of bloating your main js file that contains your navigator with buttons. It's cleaner to just inject buttons on-demand in any page that you need.
//In the page "Home", I want to have the right nav button to show
//a settings modal that resides in "Home" component.
componentWillMount() {
this.props.route.navbarTitle = "Home";
this.props.route.rightNavButton = {
text: "Settings",
onPress: this._ShowSettingsModal.bind(this)
};
}