Just go to single player-- random map, set up to your likings ( peace time, options, nations,AI,...), start the map. Exit
Go to editor and there are always 3 RNO files in your cossacks directory.
One of them is the map you have just generated in single player. They are automatically stored there.
So if you generate 3 maps in a row, those 3 RNO maps will be the last 3 maps you generated, just look at the date & hour of the map to determine which one is the one you last created in single player.
Do not change the start positions in the editor, do not change nations from one place of the map to another.
RNO maps are limited, its far better to create new maps, but then you won't have peace time, unless you script it.