Considering my options, I've decided that the best way to add new, explorable, and content-filled territory beyond Skyrim's borders is to create a brand new worldspace^1., rather then to try and adjust and modify the existing landscape beyond Skyrim's invisible border. However, the content I am planning is not far from Skyrim's border, and to be as lore-friendly as possible, I would like to use the extant terrain provided by Bethesda as a starting point.

Here is the area on the Skyrim world map: http://cloud-2.steampowered.com/ugc/540684781227546684/D193B36308E134D55A85C79C8D6CAAC230A9A731/
An in-game perspective from the south, looking north: http://cloud-2.steampowered.com/ugc/540684781222721822/F6812EF513C3A3D8EADF060D7D21A38ED9611E66/

Now comes my conundrum. Assuming I know the cells I am dealing with, is there a way to export their data into a new worldspace of my choosing? And if so, how do I go about doing this (a link to a tutorial would be fine). This is rather new territory for me in the Creation Kit, so I'm about as dumb as a rock.

1. Of course, I'd love to do it in the existing world space, but from what I've read that will make a few things more difficult. But I'm willing to give this a go if you think it would work. I'm guessing you'd start by changing the game's preexisting borders to encompass the area you want to add, as well as unlocking the map camera and getting rid of the map's heavy cloud cover in the area. Then you'd make the area its own region, apart from neighboring Falkreath Hold. Then you'd have to upgrade the rapidly degrading textures...