Import Terrain using DatGen

[Mootilda 76]

I am trying to find a solution for a friend.  She wants to edit the terrain in an .SC4 file, to eventually import into a neighborhood in The Sims 2.  She only has the SimCity 4 base game, but the .SC4 file was created using the Rush Hour expansion pack.  This means that she is unable to edit the terrain in her copy of SimCity 4.

I thought that I might be able to solve her problem by using DatGen to export the terrain from the Rush Hour .SC4 file and then import it into an empty base-game-compatible .SC4 file.  Exporting was fine, but I'm not sure how to import that data into the other .SC4 file.  (I exported using "Export Files..." from the context menu (right-click) when viewing the Elevation Map (Terrain instance 1), but "Import Files..." from the same context menu doesn't do anything at all (no file dialog).

So, I suppose that the first question is whether this is a reasonable approach to the problem?  In the Sims 2, the neighborhood terrain record format hasn't changed at all between the various expansion packs, so we are able to replace the entire terrain without any problems.  I am making an assumption that the elevation map in SimCity is also likely to be unchanged between the two versions.  If no one know the answer, no problem... I can test this myself.  [update: Yes, this works, once I get the extracted terrain imported into the new SC4 file.]

My second question is how do I import an Elevation Map (Terrain instance 1) extracted from one .SC4 file  into a different .SC4 file, replacing the existing terrain? [update: I was able to remove the existing terrain using DatGen and append the extracted terrain using a set of utilities created for the Sims 2, but I'd still like to understand how to import using DatGen.]