After testing, still not worked so used the vSphere API to read then write the UUID in instead:
<?xml version="1.0" encoding="utf-8"?><soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><soap:Body><ReconfigVM_Task xmlns="urn:vim25"><_this type="VirtualMachine">*VmId*</_this><spec><uuid>*newUUID*</uuid></spec></ReconfigVM_Task></soap:Body></soap:Envelope>