You can always dodge (lighten) and burn in (darken) non-destructively by creating a duplicate layer and working on that layer not on the original or background layer. But if you want to change the effect, you have to do it the whole layer at once.
This trick works just like painting on a mask: you can reverse the effect by switching the colour (black or white or a shade of grey) that you're painting with. Here's how it works.
Open an image you want to work on and create a new layer
Here's how it works. In overlay mode (or soft light), blending 50% grey with your image has no effect. However if you LIGHTEN that grey, it SCREENS your image, or lightens it. If you DARKEN the grey, it MULTIPLIES the layers or darkens it.
Use a brush at relatively low opacity (say 20%)
Paint with white, or lighter grey, in those areas you want to lighten.
Of course, you're looking at your original image while you're painting. If you turn off all the other layers, here's what the overlay layer might look like after you've painted on it:
Want to lessen the effect? Switch colours (the "X" key will toggle between the foreground and background colours) and paint over the area you want to change. Don't like what you've done? Paint with 50% grey and the changes are gone.
This works for saturation too! Not quite the same way, though. Create another blank new layer, and change its blend mode to "Saturation".
ANYTHING you paint on that layer will reduce the saturation of what's underneath it – doesn't matter what colour you paint with. Use a low opacity brush and paint over the offending brightly coloured bit. If you do too much, use the eraser tool on the saturation layer.
A really slick method of non-destructive dodging and burning that gives you precise levels of control, and it's easily reversible.
Here's an image I shot today that I used this technique on:
This image itself wasn't that simple. It was a 5-shot HDR created in Photomatix Pro 4, then imported into CS5. These were slow exposures shot at ISO 100, with an 8x ND filter on the lens and aperture set to f/29. Shutter speeds ranged from 1/13 sec to 1.3 seconds. I selected the water and put it on a new layer and then applied Topaz Adjust 4 smoothing to it. I selected the underlying layer (everything else) and applied Topaz Adjust but in detail mode to that layer to bring out some sharp details. I did the dodging and burning I described above. Back in Lightroom, I used the adjustment brush to further soften the water, and we're done.The rock in the foreground was too dark so I dodged it. The embankments in the distance were too light, so I burned them in. The orange leaves near the bottom were too brightly saturated. The rock face on the right needed to be darker. I made all these gentle changes by painting on the Dodge & Burn or the Saturation layers I created. The whole thing took 5 minutes, not including doing screen captures for this article!
I'm not sure I got the effect I really wanted, but it's pretty close to what I had in mind.