Hello and welcome to the forum 🙂
Yes it it possible - but please don´t do it. The way r3 is designed, you do not make changes to apps from other people. Docs: https://rei3.de/en/docs/builder#building-on-applications
Any change you make to the original app will be overwritten, if you ever install a newer version. To safely "build-on" apps from other people, you create a new app and then add your changes. In your own app, you can add data and build different UIs, while still accessing the original entities (like tasks).
In this case however, it might be more straightforward to create your own task app. REI3 Tasks (the app from the repository) has a certain permission model and work method in mind that probably does not fit well with what you describe. It is possible to make these changes in your own app, but working against the base configuration is usually more effort than building a new app that works exactly as you need it to.