If you're adding new information, I don't see why you shouldn't. For example, getting a promotion at the law firm you work for is a big deal, and then you could throw in the other stuff while you're at it. But I wouldn't just send it if there's nothing that has changed since you initially sent in your app.
If only I didn't have any "If only"s
I say go for it. It's not going to hurt your case to send the addendum. Most Adm Comm will look at it and see that you are really want to get in. If you don't send it, you'll live the rest of your life (that may be a bit of an overstatement) wondering how things would have panned out if you had only went with your gut feeling.Think about it this way, "What are you losing by at least trying?"