Is it possible to release an update to an iOS app on iTunes Connect only to certain countries, while the app has been available worldwide? The intention is to release the new app gradually on a country per country basis.
At least at the moment there is no functionality in iTunes Connect to restrict the country of an update. Furthermore, you cannot make country restrictions per version, only for an application as a whole.
You might adjust the country selection when releasing the updated version, but that would effectively remove the application from deselected countries altogether.
Anyone who already purchased your app will still be able to download it.