I had the same issue and the only way i could override the backpress behavior on both platforms is to replace the left back button with custom button and use the BackHandler of react native for the hardware button in Android. The code is as below.

Component A

//Navigate to component B from A
Navigation.push(this.props.componentId, {
component: {
    name: 'ComponentB',
    options: {
        topBar: {
            leftButtons: [{
                id: 'backPress',
                text: 'Back',
                icon: require('backbutton.png')
            }]
        },
    }
}
});

Component B

import React, { PureComponent } from 'react';
import { View, BackHandler } from 'react-native';
import { Navigation } from 'react-native-navigation';

export default class ComponentB extends PureComponent {

constructor(props) {
    super(props);
    Navigation.events().bindComponent(this);
}

componentDidMount() {
    BackHandler.addEventListener('hardwareBackPress', this.handleBackPress);
}

componentWillUnmount() {
    BackHandler.removeEventListener('hardwareBackPress', this.handleBackPress);
}

navigationButtonPressed({ buttonId }) {
    switch (buttonId) {
        case 'backPress': {
            this.handleBackPress();
            break;
        }
    }
}

handleBackPress = () => {
    //Custom logic

    //Go back if required
    Navigation.pop(this.props.componentId)

    //Stop the default navigation
    return true;
};

//Render component
render() {
    return (<View></View>);
}
}

This is Cherniv's answer. But basically what' he's saying is that every tab has an index. From 0 to N.

So by doing this will achieve it.

this.props.navigator.switchToTab({ 
    tabIndex: desiredIndex 
});

In the meantime, Kudos to him for helping me aswell. Thanks @Cherniv.

As of v1, there are a few id's that are reserved by RNN. When any of these id's is used, the custom icon passed to the button params is ignored. From the docs - four button types are supported by default without the need to provide an icon. You can use any other id and that code should work, but you'll need to handle the button press your self (call pop from onNavigatorEvent)