Migrating Identifier from non-team prefix within single account

Hello,

In our Account we have an iOS app with an explicit identifier "ABC123.com.some.app" that is using non-team prefix which is DEF456. It has also explicit identifiers for Widgets bundle and Notification Service.

Due to non-team prefix, it can't access e.g. shared keychain and data put there by our other apps. Since we are working on features that require these capabilities, we would like to update the app identifier, so it is prefixed with our team id DEF456.

Initially, we thought that the process would require steps like:

1. Create new app, team-prefixed identifier(s) for app and all things that need them
2. Recreate the provisioning profiles with new App Identifier
3. Roll out the app using with new profiles via App Store

but when trying to create the new identifier with com.some.app and team id prefix DEF456 we are getting following error:

An App ID with Identifier com.some.app is not available. Please enter a different string.

Can anybody advise us how to correctly perform such change and what steps are required from our end?

We would like to keep our existing App Store entry, ratings and smoothly switch users. We are aware that this kind of migration results in loss of Keychain access.

Thanks for any advice on that!