Android : How to programmatically enable and disable default dialler preference on the fly, like in Google Voice?

I have found the following articles but they all mention adding the code to AndroidManifest.xml before running the code. I want to be able to enable / disable the default dialer application while running the App. Just like how Google Voice does it by allowing user to enable or disable from their application.

The links I found are

How can I add my application to the android default Dialer selection?

how to use android.intent.action.CALL_PRIVILEGED and android.intent.action.NEW_OUTGOING_CALL?

Android dialer application