Thank you, smaffulli! That just might do the trick.
I tried what you suggested last night by editing from within the Control Panel, but I wasn't patient enough to let the script apply the change and called it a night before the script ran. I checked today, and it certainly does have the custom message in Firefox on the Authorization Required pop-up window.
It still would be nice to know how to modify the field labels, but this will suffice.
It appears, however, that Chrome and ID do not display this custom comment, so I will have to test this further.
Thanks a lot!