I'm sure it's possible as I've modified zones/character models. Also they made retextures of Classic-Velious zones to be higher definition and released it as a downloadable pack. (And it's packed by default with SoF-Underfoot.). It's possible to change the size of textures so long as the ratios stay the same.
I don't know how they did it with Skyrim (Like the High Def civilian clothes etc as i use those mods too heh) but I'm pretty sure to increase the appearance you would mostly have to completely rebuild the texture from scratch. You can remove data that's there but you can't make what isn't there just appear, you know? =/
If you want to try though, here: (This is for editing race models but zones would function similarly)
http://www.peqtgc.com/phpBB2/viewtop...t=9313&start=7
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