The type of a property can be changed from one type of collection to any other type of collection (external key dictionary, member key dictionary, array, or set). These changes require that any existing exclusive collections be converted to the relevant format.
Changing a collection from exclusive to shared results in the creation of a new instance of the shared collection and the contents of the exclusive collection are copied to this new collection. The reference in the parent object is set to this new collection.
As changing a collection from shared to exclusive does not automatically copy the contents to the new exclusive collection, you must do this after the reorganization has completed.