When a device-driver system is WHQL certified, the parameters of the device are obtained through inf file. As you would know in advance, VID/PID combination is unique for each product. So the digital signature obtained will be valid only for VID/PID combination present in the inf file at the time of certification. To provide signed driver for each customer, we have to run test using the inf file and device of each customer. This is not possible. On our part we run tests and take care that CyUSB.sys is WHQL certifiable. Getting the device-driver system certified is the responsibility of the customer.