How to notify users that accepted a CKShare with Write Permissions about Changing Access Controls on User (Owner) Data?

I use iCloud Key-Value Storage to keep the info about if the privateCloudDatabase has been restricted or not.

If the user restrict the database:

    let ubiquitousKeyValueStore = NSUbiquitousKeyValueStore.default
    ubiquitousKeyValueStore.set(true, forKey: "PrivateCloudDatabaseRestriction")
    ubiquitousKeyValueStore.synchronize()

If the user unrestrict the database:

    let ubiquitousKeyValueStore = NSUbiquitousKeyValueStore.default
    ubiquitousKeyValueStore.set(false, forKey: "PrivateCloudDatabaseRestriction")
    ubiquitousKeyValueStore.synchronize()

In other devices for the same user (diferents for the one that enable or disable the restriction) the user is notify using the following code:

    let ubiquitousKeyValueStore = NSUbiquitousKeyValueStore.default

    override func viewDidLoad() {
        super.viewDidLoad()
        NotificationCenter.default.addObserver(forName: NSUbiquitousKeyValueStore.didChangeExternallyNotification, object: ubiquitousKeyValueStore, queue: OperationQueue.main) { (notification) in
            print("NSUbiquitousKeyValueStore.didChangeExternallyNotification")
        }
    }

In case that the previous user send a CKShare with write permissions to others users, How can this users by notified if the owner of the privateCloudDatabase enable or disable the restriction?

Also it is possible for the owner of the privateCloudDatabase to check at any time the status of the restriction

let ubiquitousKeyValueStore = NSUbiquitousKeyValueStore.default
let privateCloudDatabaseRestriction = ubiquitousKeyValueStore.bool(forKey: "PrivateCloudDatabaseRestriction")

How could check an user that accepted a CKShare with Write Permissions the status of the restriction made by the owner of the privateCloudDatabase?