ydopen, they can not ticket you for taking down your rear view mirror as long as you have 2 other reward facing mirrors that are not blocked by something. What is the difference if you have the center rear view mirror blocked by a full load of boxes or not having it at all? This is the same basic idea why full size trucks have to get the mirror extenders for hauling big loads. They have to be able to look around the rear of the trailer.
Depends on state law....
In Illinois the law is 'one mirror capable of vision 500 foot behind the vehicle.'