I descended into hexeditor hell and had some success. I managed to change plains to Desert with the hexeditor (5 changes). I know you can do that in the map editor, but I wanted to test the principle. I then started a game and saved it before I founded a new city, then again after. there are 94 difference in the relevant section of the .sav file, which will take some time to sort out.
For non-newbies only: What I have learned is this, if you look through a .sav or .bic file you will find at the bottom sections of data about your cities (in the order they are founded), however the location of your cities on the map are not stored here. Rather that information is stored in the lengthy section above regarding the "Tile", i.e. the spaces on the map. To reduce complexity I used a 16x16 space map (the smallest allowed -- and man it creates some annoying problems in play testing), to give me 256 "tiles" to deal with. The tiles seem to be listed in pairs with the first one shorter than the second (I don't know what this means). It's not much, but over time it may yeild some good things.