In Navisworks you can change the Avatar that appears when viewing the model. To change the avatar go from the Edit Viewport Settings button to the Collision Settings and change the Avatar from the drop down.
Human 2 comes with a hard hat.
You can make a new Avatar by putting it in the C:\Program Files\Autodesk\Navisworks Freedom 2011\avatars folder. An avatar model needs to be created for each portion of the crouch, which is 5 models. I copied each one and made my own. Instructions are also available in Help.