I have created a hello world component based upon this documentation https://docs.joomla.org/Special:MyLanguage/J3.2:Developing_an_MVC_Component/
I want to send a notification to users if an item's publishing status has been changed.
I found the function
Can we override this function in my custom component?
I would suggest you look at creating a plugin to send the email that responds to a onContentChangeState event trigger. The plugin would check that it is an item of your component being changed($context in the params) and then it will provide the ID and the value(Published/Unplublished) that you can use in your email subject or body.
This should be a starting point for you, https://docs.joomla.org/Plugin/Events/Content, third from the bottom.