Their was one thing I wanted to do, and found out, that I am unable to. I was hoping to go into the material room, and put a transparent image file on "Main Camera" for animations. Like crosshairs and calculating (Distance) numbers, and color green (night vision).  I know most will say.."Just put a flat square in front of camera, then texture that. Yes, but if I have to move camera around for an animation scene, and that alone. I want to texture on camera, not another prop. Would be easier...wouldn't it? How can "Main Camera" be textured?

Put the square in front of the camera, then parent it to the camera, and then lock the square. Animate at will.