How do I correct errors in album/work/song/track in Gracenote after the CD is already imported into iTunes?
Aha!  If I turn off the eject after import option (which the latest update turned off without asking me!), then the import window stays there and I can continue to edit and submit.

Or, I can say No to the import, do my editing, submit corrections, then Import.

Third option, re-insert the CD, make corrections, submit, re-import (it will ask me whether I want to replace the previously imported files).

(Unfortunately, it won't let me edit some tags, but that's another question.)