I'm not sure once a pax loses Mosaic status, does B6 have the IT processes in place to update the PNR so it no longer reflects Mosaic to an agent?

If not, you might be able to do a same day change or check bags for free.

However, even if the PNR doesn't update, you might have a hard time callin in for free changes & cancels:
1. I think general reservations agents are told not to touch a PNR for a Mosaic; and
2. When you call the Mosaic line, you can't even get to a Mosaic agent until you enter in and the system validates your Mosaic TV#. If you don't put in a valid Mosaic# you get routed out to general reservation sales.

I'm not sure though maybe you could do a change/cancel on the web site.

that being said, they very well may have a process to sweep all the PNR's and update status. Although, B6 isn't known for its rock solid IT, so you have at least a 50 50 chance they don't have the IT mechanism to sweep all the PNR's.