For each account pair AUTH_xyz and KEY_xyz, you'll need to copy every container and object from AUTH_xyz to KEY_xyz, then delete AUTH_xyz.

Swift uses a hash of the entity name (account, account/container, account/container/object) to determine placement of the entity on disk. Renaming an account thus changes the hash of everything therein, and so requires a copy-and-delete of everything in the account.

Note that though I've said "rename", Swift's API has no such operation. To "rename" something is really to copy it and then delete the original.

Side note: from the standpoint of getting your cluster working again, the fastest way is to put the reseller prefix back. It's just an arbitrary string. Even if you're running multiple auth systems, just ensure their prefixes don't collide; that's all.