Hi Sam,
The unconfirmed images in that source should automatically get reannotated.
Specifically in terms of the source's background jobs, once you submit that change, CoralNet should schedule a source-check job.
Then during that source check (assuming there's nothing else to do like feature-extraction or training), it'll look for unconfirmed images that were last visited by a classifier other than the newly-selected classifier, and will schedule those images for reclassification.