The official line on this from Apple in their iTunes Connect FAQs:
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Q: I sold my app to another developer and can no longer distribute it on the App Store. Can I transfer the app to the new developer's iTunes Connect account?
A: No, you can’t transfer the app to another developer account on iTunes Connect. To add the app to another account, remove the app from the current account and upload it to the new iTunes Connect account.
Note that uploading the app to a new iTunes Connect account will disable current customers from receiving automatic and free updates of your application. All customer reviews, rating, and ranking information will be reset. You will not be able to reuse the app name and SKU in the old account. If you have uploaded a binary or used the app with the iAd Network, your Bundle ID will not be reusable either.
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I have no idea if special exceptions are possible, but that is their official policy:
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Q: I sold my app to another developer and can no longer distribute it on the App Store. Can I transfer the app to the new developer's iTunes Connect account?
A: No, you can’t transfer the app to another developer account on iTunes Connect. To add the app to another account, remove the app from the current account and upload it to the new iTunes Connect account.
Note that uploading the app to a new iTunes Connect account will disable current customers from receiving automatic and free updates of your application. All customer reviews, rating, and ranking information will be reset. You will not be able to reuse the app name and SKU in the old account. If you have uploaded a binary or used the app with the iAd Network, your Bundle ID will not be reusable either.
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I have no idea if special exceptions are possible, but that is their official policy: