I have already submitted the Windows Phone 8 app to the windows phone store. Got new requirement to submit the same .xap with the same name to the app store with different Developer ID. How can I do that? We want both the apps to be present. Also is it possible that existing users can upgrade the app after it is submitted by new Developer ID? can we notify users by giving new link for the app from another developer ID(If it's possible to put another app using new developer ID)?
I don't think you will be able to submit the app with the same name even you are using a new Developer ID since you have to associate your app with the store, where the App Name should be unique. Yes you can push an update for the existing app by selecting Update App from the Dev Center.