This is just a simple script that you can use to add (yes) and not replace objects to your Onset game server. This piece of code is untested but might be a good base to develop something like this.
This is possible as of Onset's version 1.1.0 which removed the restriction of using valid game object model IDs, this was made for such scripts to be possible.
The game has 1843 objects to be exact as of writing, so a good practice would be to use all your custom objects to follow the model IDs of above 5000 to keep it future-proof until we can have a more robust solution in the game for something like this.