For the SimplifiedModding_Tartosa-Hiders is there a way to remove the buildings... or maybe replace them with something more old world. Ugh, I hate them!
Yeah you could definitely remove them using the method in my hiders tutorial like any other world deco object. Any world terrain paint would stay behind though, leaving it pretty unsightly, though.
Replacing them is basically the same as that, too, except instead of deleting the model and footprint entirely, you'd replace those with the ones of the shell you wanted to use instead. The hardest part is really finding or creating a mesh of suitable size/shape to replace with, since if it's too big, it can overlap, or if it's too small it can look pretty weird.
Best bet (without meshing) might be to try some of the deco shells from Windenburg or Henford on Bagley and see if any of those can fit. It'll completely change the look and feel of the world, but might work.