Some responses to above:

1). If you cancel an itinerary with MTM you get the certificates restored. Best way to assure it happens immediately is to call and have them remove MTM which you can do at any time. Then cancel

2). I believe MTM only applies to one companion but i
did not research to verify. Perhaps I just assumed because that is how every normal airline operates.

3). Continually annoyed with Jet Blue. If the fare changes on just about any other carrier (maybe not AA) whether paid or award, even if I have been upgraded I can have ticket reissued and get the difference back as credit. Some carriers I can do this online myself (Delta for example). B6 - I ticket at 24,300 points per person. Confirm MTM. 3 days later fare is 18,000, so for two pax overpaid 12,600. Can’t change award travel - have to cancel and rebook. Mosaic desk can’t tell me how many certificates will be needed for new itinerary if I cancel and rebook without an existing reservation by a mosaic who has enough certs. So do I risk losing mint trying to get my 12k points back - of course not. Another reason this system is so poorly deployed and not customer friendly! I sent them a message asking for something as a customer service measure but not hopeful they will make this right. They probably don’t even see anything wrong with their IT.