In App Center, you upload an app and apply an app policy to "wrap" the app. In the app policy, you elect to create new keys for the app. You later remove the app policy ("un-wrap") and then replace the app with a new version. When the new version is uploaded, you see an error similar to:
The new version of the app has a different certificate than the old version of the app. Android prevents the upgrade due to the certificate mismatch.
The device user must uninstall the old version of the app before the new version can be installed.