[ctide]

I'm not modifying a list there, I'm modifying the privacy settings of a wall post I'm in the process of making. When making a wall post, there's a little padlock and from selecting the customize option, you can target an update to a list. In this specific case, See Everything is a list I've created. Adding people to that list after this update has already been posted does exactly what you describe, it allows me to maintain just that list and they sell all previous and future things that I limit to it. While I don't use this much for status updates, I use it heavily for restricting photo albums.

It's also not for all wall posts unless you check the box at the bottom of that dialog setting it as the default.