This is indeed a good news for all existing PTP820 customers.
In brief. For customer who RMA their PTP820 radio, customer can transfer the existing keys from the RMA radio to the spares.
Details about the process can be found in this DN, or you can call the customer support when you RMA the PTP820 radio with Cambium.
DN-1357 PTP 820 License Key Entitlement Refund Process