Hello,
You can allow the notification style to be changed by adding an activity to the configuration. Go to the configuration settings to the MDM Settings tab. Add to allowed activities:
com.android.settings.Settings$NotificationAppListActivity, com.android.settings.Settings$ConfigureNotificationSettingsActivity
Now you will be able to change the activity style through the lock screen via the Notification Settings button.
With this method, other settings will remain unavailable to the user.