After you have imported the model back into Inventor, you have a solid model that you can edit further using Inventor tools.
Import the assembly into Inventor:
The modified blade clamp appears in Inventor, along with the new connecting parts you created.
Use Inventor to edit the new parts:
Inventor opens the Fillet dialog. Leave the settings unchanged to accept the defaults, but set up filleting by clicking the rear edges of the U, both inside and outside. Click the front corner edges of the U-clamp as well.
Inventor fillets the edges you clicked.
If you want to experiment, you can fillet edges, or make other edits, to the original blade clamp object as well.
In this tutorial, you saw how you can use the SAT format to share objects between 3ds Max Design and Autodesk Inventor, and edit them in either application.