Originally Posted by Microsoft
When hardware components are changed, Microsoft's product activation process compares information derived from the initial validation, which includes the hardware configuration of the device, against the changes that have been made. This process uses an algorithm to help assess whether the software is installed on the same device. Validation will fail if the software detects a substantially different hardware configuration.
At that point, the customer is able to use the one reassignment for the new device. If, after using its one reassignment right, a customer again exceeds the tolerance for updated components, the customer can purchase an additional license or seek remediation through Microsoft's support services.