Hi there,
Thanks for your suggestion. Staff can switch off application links on a per-service basis using the "Manage App Links" Module Command button under the client's Products/Services tab.

As this idea hasn't gained traction in the 2 years since it was created, we are declining this request at present. If your clients have their own sub-clients, then they should consider switching to reseller level hosting (something fully supported by WHMCS) instead.