SSE how to add landscaping/locations/mobs to terrain outside skyrims borders?

[KappaMeister]

I've been meaning to get back into modding Skyrim after a long break, and I have an interesting idea for a mod to try and make. As you might know, Skyrim's world is detailed but not very large compared to other modern open world games, but there's quite a lot of heightmaps and basic LOD terrain outside the games playable borders that encompasses much of Cyrodiil and beyond. If i recall correctly, some of these out of border locations (particularly those east of Riften) have trees and foliage but no mobs of navmeshes, and if you've seen the videos talking about the while gold tower model found outside the games playable area you'll know what I'm talking about.

 

I want to make a mod that fleshes out these areas of terrain outside the games borders that already exist by adding navmeshes, detailed scenery/landscaping, and potentially enemies and locations to explore. This won't be a massive game expansion in the traditional sense; it simply aims to add more explorable and fleshed out terrain to Skyrim without adding that many new quests or hours of gameplay and remaining below the maximum cell size before the infamous Havok physics bug triggers. I also plan on installing a mod that disables the invisible borders entirely so that I won't have to worry about editing the parameters for that in the CK.

 

Unfortunately, most of my modding experience comes from scripts and adding new spells/items and the like, so I'm not very knowledgeable with landscaping and world creation. I just haven't found any tutorials online that cover what I'm trying to do; there are plenty on creating new worldspaces with their own cells in the style of Falskaar, but virtually nothing on adding to and changing the landscape in the Tamriel worldspace. In addition, I'm not even sure if the out of borders terrain in the Skyrim worldspace is even editable, as I haven't been able to access or even see it in the CK and I'm not sure how exactly the game treats it compared to more fleshed out exterior cells. Is it just heightmaps? or is it real terrain that I can some how edit in the CK like any other cell?

 

So can anyone tell me what I'll need to know in order to edit, expand and flesh out the out of borders terrain found in skyrim like any other exterior cell? How would I go about editing the Tamriel worldspace and it's terrain/landscaping like with a new exterior cell? Are there any good tutorials on this sort of world creation and landscaping and their cells out there? And if this sort of mod isn't even possible, how would I go about adding new terrain beyond Skyrims borders manually while getting it to work properly?