There are always some of exchange for partical objects in DGN file. Existing work flow for part of objects to dwg file:

1. Select objects to be exchanged

2. Set DisplaySet

3. Draw a Fence

4. Use "Copy Fence Contents to New File" Tool to copy them to a new DGN file

5. Open the new DGN file

6. Save as DWG.

That would save the "opening" and "save as" times if the Copy Fence Contents to New File tool could directly copy them to DWG file.