Glad to spend more time.
I've already created a test library and have tried a couple of things. Calibre help info indicates that the plugboard works "when saving to disk or sending to device".
I tried saving to disk (my desktop) and the author changed from "calibre" to today's date. However, downloading to my Nook did not change the author at all.
If any files from within the EPUB container saved to the desktop would be of any help, let me know.
G ... the ball is in your court!