you have to find an agent that knows about the secondary system and WILLING to swap it out for you. Basically cancelling the current certificate and repurchasing the residual certificate for the same cost as the one that is cancelled. Previously the cancelled certificate has a residual refund equal to the reissued certificate. Not sure now. As for waiting until closer to expiration to call (if Marriott doesn’t auto extend another round), if you are good with losing the certificate, then wait. I personally will just use it locally for a staycation and write it off as a pandemic loss. But one thing is for sure, there will be lots and lots and lots of complaints when Marriott doesn’t extend (I take that back, even if extended, the complaint will be that the extension is not long enough). I guess that is the game.