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What happens to the existing customers who already downloaded and using the app? (While the name change is ongoing)
Nothing will happen to the customers.
What happens new customer wants to download the existing app while the store account is under review for the name change?
They will download your app which is still in the old publisher name.
What happens after I re-package the apps with the new publisher name? Will that go as an update to existing customers?
If you submit a new submission on the Store for the new package, then the answer is YES, the customers will receive an update about your issue and the publisher name will be updated.
If a customer side-loaded the old app and the new publisher-named app, will that install 2 apps?
Yes, when you changed your publisher name, the Package Family Name of the app will change and the system will consider them as two different apps.
How long will it take for the name change to take effect? (Roughly)
There is currently no clear time for this.
What happens to the existing apps in the store which were not re-submitted with a new package?
I'm not sure about that. But I think they will need to be updated. You could open a free support ticket about this issue: Contact Us. Go to Contact us, find Non-Technical Support - Dashboard and choose CHAT NOW or **
SUBMIT AN INCIDENT**. You could talk to the store team directly and confirm this behavior and ask the impact of changing the publisher name.
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