Hello,
The nature of Symantec App Center, is that it creates an alternate app store to allow the management of apps outside of the standard device's app store. The Symantec App Center client is a mobile device app which provides a portal for end-users to install apps that are managed and provided by the Symantec App Center administrators.
In the current version of Symantec App Center, you cannot disable the default app stores. However, in the next release (version 4.1), there is the ability to disable the Apple App Store on iOS devices. Disabling the Google App Store (Google Play) is not yet supported.
The only possible way to manage pre-paid apps is using Apple's Volume Purchase Plan (VPP). The app is purchased through Apple, for the desired number of licenses, and the app can be made available to App Center users using an "External Store App", which is essentially a link to the app within the Apple App Store. It is not possible to deploy, or manage, paid apps from the Google App Store.
Let me know if this answers your questions
Thanks,
Andrew