Is it safe to change the AppID Prefix between updates?

My conclusion, as of today, is that it is completely safe to replace the AppID prefix by a new one, with the exception of apps using the keychain. This opens up for migrating the prefix for all my exiting apps on the App Store to the new TeamID based prefix.

This conclusion is based on the following input:

• A discussion I had with Apple's developer support a couple of weeksago. They told me that there should not be any problems changing the prefix, except for apps using the keychain.
• A test I did, using ad-hoc distribution, verifying that an existing app on a test device did not lose any data when it was updated to a new version with another prefix.
• The fact that I have successfully uploaded new versions, with replaced prefix, of twoof my existing apps without any problems so far.

The status of the two "live" apps that I have changed, is that they have been approved in the review. However, they are currently waiting in "Pending Developer Release", since I am waiting for a third app to get ready in order to sync the release with that one.

If I see any kind of problems when they go live on the App Store, I will of course update this answer.

Update:

The two apps were released successfully more than three weeks ago. The roll-out worked as expected and I have not received any user complaints.

In summary, the answer is YES, this is completely safe!

Apple published a new tech note on February 12th 2014 confirming that it's possible (and safe^*) to change Prefixes yourself for Wildcard App IDs, but it's still impossible to do it yourself for Explicit App IDs.

However, they say you can contact member center maintainers if you would like them to change your Prefixes for Explicit App IDs.

Gonna include this part here in case they change their mind again:

All other App IDs will require the assistance of the member center maintainers - if you are not using a wildcard App ID, then you should contact the iOS member center maintainers for assistance. Here are the steps you can use to do that:

1. Go to https://developer.apple.com/contact/.
2. Submit a request by clicking the link under Enrollment and Account.

^{* Keep in mind that if your app stores data in Keychain, changing app ID prefix will result in one-time Keychain data loss.}