The actual layer will look like this, when you turn off the
original Background layer (by clicking on the eye in the layers palette).
Wherever it is 50% Grey there is no change, otherwise the Soft Light
Blending mode with lighten or darken as appropriate.
You can always paint in 50% Grey (RGB 128,128,128) to undo you changes.
The other thing you can do is change the Opacity of the Layer to reduce
the overall effect.
Incidentally you can also paint with colour to bring out some of the
hidden colours in the picture or to tint it.
If the effect if not strong enough, consider changing the blending mode
to Overlay.