Expand on existing export

Hi.
I'm wondering if it is possible to expand on already existing exports, so that I can keep making local exports with bouns and keep filling in a larger area. By doing this i want to build up a database for the world piece by piece.
An example:
I've exported 2 separate parts of a country (elevation Binary Terrain in this case). Now at a later stage I want to export the rest of the country without reexporting the already existing elevation data.
Is this possible, and if yes, how can I set it up?
I'm wondering if it is possible to expand on already existing exports, so that I can keep making local exports with bouns and keep filling in a larger area. By doing this i want to build up a database for the world piece by piece.
An example:
I've exported 2 separate parts of a country (elevation Binary Terrain in this case). Now at a later stage I want to export the rest of the country without reexporting the already existing elevation data.
Is this possible, and if yes, how can I set it up?