The instructions are in this thread: http://forum.xda-developers.com/showthread.php?t=1162693
All was well, but a lot of my books are sideloaded and I've disliked that my sideloaded books never appeared at the front of the list when sorted by Most Recent. They would always be several pages back, behind my most recent B&N purchases and some would be on random pages even further back, actually. Yes, this is truly a first-world problem, not particularly important in the grand scheme of things, so I didn't really complain about it - nor did I ever really try to fix it. I'd just silently curse every time I tried to find a new book to read.
Anyway, a friend bought one for her grandmother, and wanted me to write specific instructions for registering it; yes the procedure is step-by-step, but it was for Grandma, so I unregistered my N2E and reregistered it. Typing out exactly what, where, when, etc... and emailing that to Grandma. (Grandma later responded that she was grateful, but probably didn't need the step-by-step instructions.)
Anyway, this got me to thinking. Was there a way to skip registering? Would it truly arrange my books by date? I did some googling, found that info up there and tried it.
It did. I've sideloaded most of the books that were previously on NOOK, including my B&N books. I had to enter my credit card the first time I opened one, but beyond that, it all works flawlessly. My books arrange by date as I'd like them to, by author, by title, etc... Newly added books come to the front as (I believe) they should. Everything works.
The home screeen is different, though; I no longer get recommendations at the bottom because it's not registered and in the "recently added" listing to the right of the "Currently reading" book, there's nothing because there's no B&N content as far as N2E knows. I also can't share to facebook or Twitter, but I never did that anyway, so I don't miss that.
I'm sure that everyone already knew this, but it was a pleasant surprise to me and I'm glad I did it.