We use a BOOT_COMPLETED BroadcastReciever to detect when the user updates to O in order to initialize notification channels.

To avoid listening for boot completed when we don't need to, we could only enable it on O+ via the manifest 'enabled' property & a boolean in resources which overrides on 26+, and disable it when it's not needed any more via 
https://developer.android.com/reference/android/content/pm/PackageManager.html#setComponentEnabledSetting(android.content.ComponentName, int, int)