The tariff loaded from the database is protected against any change by your drivers. The Taxi Company Manager will own the user-id and the password to do any tariff changes.
If you have for example a ‘Night’ and ‘Day’ tariff, your driver will not be able to do a manual selection. The app will automatically choose the right one and prevent any change.
Similar for week-end tariff on a workday.
You can block the usage of the app after driver has logged out.