There would be a substantive difference between a consent stop and search (checkpoint) and a SPOT stop.

A consent search can be stopped at any time up to the point the officer finds something that elevates the consent search to a non-consensual level (reasonable suspicion). Once that level is reached then the person no longer enjoys the right to terminate the search.

Away from the checkpoint it would seem that Terry policies apply but again, as has been noted, TSOs aren't LEOs so I must admit I'm ignorant how their function applies here. Us LEOs would definitely be bound by Terry. TSOs? Can't say.