Answer
How much this costs and how much friction it creates varies by vendor. Some handle it as a straightforward re-key once the new machine's serial number is on file. Others treat it closer to a new purchase with trade-in credit for the old entitlement. The practical step is building a full inventory of every IBM i license and entitlement tied to the current Power 9 serial number before ordering new hardware, so the licensing cost is part of the budget from the start rather than a surprise after the machine arrives.