Out of idle curiosity--is it possible to 'downgrade' a 2nd line back to a virtual number? I ask because going to the VN/2nd line page from the main account, it does not give me an option to downgrade the other line (but does ask me if I want to 'upgrade' my main line), while hitting that page from the VN account, it tells me that I'm using a sub-account and am not allowed to access the page...

I have no intent to do so (and can't imagine that I will). Setting it as a 2nd line allows me to use it as a virtual number that my * system can recognize separately from the main number. (It's always set to forward to a SIP URI.)