Yeah this has been a policy of Jetblue from the start. In fact, up until a few years ago, you could refare for free anytime after booking - not limited to the first 14 days. Of course, for Mosaics this policy essentially still exists since there's no cancelation fees anyway.

I've done this many many times in the past, last of which was last week after the fare went down >$200 a week after I booked.