This is...a long shot...but it is possible to expand regions when it is already made? I heard it was possible to have a limitless region (RAM permitting, of course) but I think it would be cool to expand regions. Possible? No? Maybe? :-\
You can easily expand your region to the right and to the bottom, just resize your config.bmp, leaving the original pixels exactly as they are
But not to the top or left? &mmm
Still though, that's a relief. Time for city super-sizing! (though I haven't touched SC4 in a year...)
adding to the top or to the left can be done, but it is a bigger, boring and tedious job
create a new region folder
create your new config.bmp based on the original config.bmp with the new size you want
then incorporate all the cities of the original region in the newly created one in the correct place
Depending of the size of your original region this can be tedious
However with some luck, I might add something in SC4Savegame explorer to speed up the process a bit( no promise here )