Can I insert an Object (obj or fbx) in a finished programme.

I want to show an object on an oculus rift sdk 2.
I built an area with an object in the middle, which I can move, rotate etc.
After that I finished the programme and get an .exe file etc.
If I want to view different objects I always have to load it in unity and create a new programme
Now I want to change the object shown after I finished the programme.
I think of something like: exchanging the object in the specific file with an object that has the same name.
All these objects are catia files, transformed into obj or fbx (with Vred)

Sure you can, you can use AssetBundles or you can use something like @Eric5h5 objreader to bring in new objects into your runtime unity application. The implementation is up to you, whether that is stream from some location on the web or from disc/perm storage on the device.