Join Date: Mar 2009
Location: NYC
Programs: AS MVPG, DL KM, Bee Six, Bonvoy Plat, Choice Plat, IHG Plat, Avis PC, Natl Exec, Greyhound Road Rwds
Posts: 20,108
Nothing can be reliably done on the website or app with JetBlue.
To cancel a ticket after checking in, you'll have to cancel your check-in, and then you'll be able to cancel the ticket itself. In theory this should be fine, assuming the website or app function properly.
If you just need to meet or escort somebody airside, you may consider asking for a gate pass at the full service check-in counter.
-J.