You can make changes to your mobile app even when it is live (or published on the app store(s)) and these updates will reflect on your app in real-time. Additionally, any updates you make to your website will also reflect on your app in real time.
Note that the only changes that cannot be made once you publish your app are:
To update these, you would need to generate a new build of your app. Once these changes have been made, generate new builds of your Android and iOS apps and submit them to the app stores.
You can also generate a new build of your app when a new feature or code version is released. Also, your app users will only be able to view the changes when they update their apps from the app stores.