You can adapt a SAPUI5 app to your specific requirements. For example, you can adapt or replace views, extend or replace controllers, or change language-specific texts.
The customization of SAPUI5 apps uses the component configuration: The customizing information is stored in a specific area of the component configuration. Such a customization can be performed on a custom app that extends a delivered standard app. A replacement or extension of views and custom controllers can also be part of a custom app, but may not always be required. If no replacement and no custom controller exists, the custom app project only contains the component definition with the customization configuration.
The standard app itself is not changed. The customized app becomes the start-up project and launches the standard app with the additional customizing configuration.
UI adaptation at runtime is currently not available in SAP BTP.