Windows Phone has a very high security level when it comes to system settings.
Microsoft does not allow apps to change system settings to protect you, the user. We asked Microsoft to allow us to ask you for allowance to change these settings. Sadly Microsoft did not allow us to create the user experience we wanted.
It is also not possible to change loudness via our app. Microsoft is aware of the fact that you as users and we as developers want to do more with the settings and settings pages.
Adding a corresponding option is currently under review by Microsoft.