Android Secure and System settings can be updated via MDZ by constructing an MDZ package that contains settings.xml file for the UPDATE_SETTINGS action. A sample management folder structure that can be built into an MDZ for this purpose is attached to this document (Settings_update_mgmt.zip). You can find this attachment at the bottom of this document. Use this sample as a reference for the structure of the directory that needs to be passed into the Management Package Builder tool as described on this page.
The contents of the sample settings.xml file is shown below
<?xml version='1.0' encoding='UTF-8' standalone='yes' ?>
<string name="notification_sound_name" value="Pixie Dust" />
<int name="wifi_watchdog_on" value="1" />