I've set up a complex scene inside a complex prop, and often when I think it's ready to render, little changes snap into place, throwing it off. somehow I moved the mouse without wanting to. could we have a LOCK SCENE feature that would look the entire scene, without having to tediously lock each part of each figure?

drawn

You can't move anything on a scene without actually clicking on it and moving it while holding mouse or yanking on a body part while holding that button. May it be that you accidentally move the camera? I'd suggest to set up one camera the way you want and then use another one for any changes you want to make.

Also, save button is your friend. Save the way you want right before you hit the render button. Done.

There is also the autosave feature.

Once you save a scene, this will save backups periodically. Then if a scene gets corrupt or crashes, you don't lose everything

You're going to have to go into each piece of the prop and lock it manually. I've tried this and it has helped a lot.