The default items, Camera, Null, and Bone can each be replaced with your own custom versions.  To do this, create models of them (in .lwo format) and place them into subdirectories with the messiah folder in your Temp directory (which is where your messiah.cfg is).

Why would you want to do this?  Who knows, but you can.  Actually, here are a couple of reasons:
     1) Make a Null object that's easier to see.
     2) Make bones that are solid, or can be viewed using any of the display modes (wireframe, points, smooth-shaded, etc.)
     3) Impress your friends.

Here's what the directory path should look like for each type of item:
For the Camera:
temp/messiah/defaults/cameras/camera.lwo

For the Null Object:
temp/messiah/defaults/nulls/nulls.lwo

For the Bones:
temp/messiah/defaults/bones/bones.lwo
Note: The shape of the bone object has nothing to do with the influence it has on the points.  It is just a visual reference.

There are samples of custom default items in the messiah_content/Objects directory.  The folder is called defaults.  Just copy that folder into your Temp/messiah/ directory and re-start messiah.  If there's one you don't want to use, just delete the object.