I have no idea how to do that, but at least it made me update my very old TES4Edit version!
Edit: I THINK I found out where to do that (the screen with the rows and columns and the XYZ coordinates) when selecting "landscape" in the "worldspace" section.
Yeah. Specifically the VNML and VHGT sections. You can drag the entire section over to where you want it and it will copy all of the XYZ coordinate data across when you do. It can result in some land tearing though, so it would be best to test on a copy of your file in case it doesn't work out. There's apparently some overlap in how LAND records work.
I was also wondering if I could use TES4EDIT to copy parts of the Tamriel world into the city worldspaces, so they will better match the tamriel world.
Shouldn't be necessary if your city worldspaces have Tamriel as their parent. Any changes you make to Tamriel landscape will be reflected in the city's worldspace.
Ah, ok - didn't know that. I'm still learning about BSA's and lod stuff, though, so it's good to know. I take it resources in a BSA cannot be used to replace vanilla ones, even if the folder structure within the BSA is identical? I'm assuming that's because of the way it parses the BSA content?
There's been some reports scattered around that a resource in one BSA cannot override resources in another BSA, and may even crash the game. So if you want to override a BSA, it has to be with a loose file.