I think you would most likely have to mod the game, which could potentially cause the game to become unstable. However, I am not completely sure as I have never dabbled in the art of modding the game itself.
If you have some knowledge with Unity, you can use the tools provided with the SDK to extract the data files, and swap your model with one of the already existing in the game. Then repack the files and the game will spawn your object. But this will only work for your computer, any interactions with this object uploaded to the cloud will appear as the stock object on non-modded games. Also this will only work with objects with no interactivity, so don't try to swap any of those objects because it just won't work.
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-Myname
Also this will only work with objects with no interactivity, so don't try to swap any of those objects because it just won't work.