" enable the users to use a specific application only"

That is not a feature of the WM 4 to 6.x OS. But it would not stop me from blocking the user from exiting my app.

So that may be the real cure. Have your app's author add the feature to not exit and keep focus on the app you want to stay running.

As an WM app author we can come very close to your goal. Then again there are folk that don't want to talk to the authors.

-> Another way is to install some app to reset it to the desired settings. Your WM app writer can do that too.

And finally you have the folk at Symbol to tap.
Bob