I don't understand what you hope to gain my changing the grid size on the in-game map.
The larger grid lines are 1.28 km X 1.28 km, because the whole playing area is 12.8 km X 12.8km in size.
Dividing this into 10 X 10 grid lines gives you the 1.28 km main grid lines, further division of each of these main grids gives you 128 metre X 128 metre grid squares.
Changing the main grid to 1000 X 1000 metres will result in you having 12.8 X 12.8 main grid squares.
Apart from changing the grid square sizes on the in-game map this will have no other effect on the game.
In fact if you do edit the games config.bin to reflect this change, you will probably not be able to play Multiplayer online on many servers which will kick you off because you have an edited config.bin........Unless you save the default config.bin and replace it when going online.
As I said, apart from changing the grid size on the in-game map, there is no other benefit gained from doing this that I can think of.
Planck