Headgrinder, I'm aware that graphics in previews don't always update. The previews share 3 image objects which are loaded with the correct gradient and tilesets. They will only load an image from file when the current image is different from the one needed. This helps to keep the program running quickly since reading from hard drives takes time, and it's only problematic if you edit gradients and tilesets while editing the level, and so, it will stay like this.
To update preview bars without restarting the program, move to a room where at least one preview bar will use a different image than the one you have edited. Then, return to the room you were working on.
For your second question, I don't intend to make any batch screen copying processes. I champion the use of
Xoft's Level Composer for this sort of thing. As you pointed out, there's no need to reinvent the wheel.
Edit: Maybe, I could force preview graphics reloads when users toggle preview visibility.