Article 63 The General Secretariat may modify the Plan and notify service providers thereof within a period of time it deems appropriate but prior to the date on which the modification is to take effect. Service Providers shall notify their customers regarding any such modification and its practical effects in accordance with any direction issued by the General Secretariat.     Article 64 Service Providers and customers shall have no property rights in numbers.     Article 65 A service provider shall only change a customer’s number in the following cases:   1.      Upon the request of the customer. 2.          A change in the location of a fixed-service customer which makes the retention of the existing number technically or economically unfeasible. 3.      Modification to the Plan. 4.      The service provider has other reasonable grounds, including compliance with any orders, decisions or notices issued by the General Secretariat, to effect such a change. In this case the service provider shall notify the affected customer in writing of the reason for and anticipated date of the change, as well as of any compensation to be paid by the service provider in accordance with Article 35 of the Law. In cases of emergency, oral notice with subsequent written confirmation shall be sufficient.   Article 66 The General Secretariat may publish instructions on practices and procedures for the allocation and assignment of numbers, including identification of any fees or charges payable by service providers or customers for such allocation or assignment. The instructions shall form part of the Plan.