Maybe this is not news, but I found out that instead of dodging and burning directly on the background layer, you can create a new pixel layer and use the paint brush (white or black) with varying degrees of opacity to dodge or burn (instead of using the dodge and burn tool). This way, the changes can be easily reversed or cancelled. Unfortunately, no amount of burning seems to make any difference on clipped highlights. I assume because there is no information whatsoever. Is the only solution to darken clipped highlights, to recolor them??