I would like to know how to export or save a model out of my dgn as a stand-alone dgn file.
Here's a neat trick. As you know, you can’t delete the default model, however…you can trick MicroStation by doing this:
Do a File > Save As… > Options > Filter > Models. Now select only the model that you’d like and save the new file. If only one model is selected, it will become the new master model.