Afaik there is no specifics on the implementation, but to me the most logical way for Google to inplement it, would be to update the setting at the OS level for installing 3rd party applications.

Google can then require any phone manufacturer that wants access to the Google Play Store and Google Play Services (which is all of them) to also push that update.

If they implement it like that, there would be no way around it other than simply not updating your Android