Shadow Highlight is a great adjustment for bringing back some of the areas that have become plugged up in our photos. The good thing about this adjustment is that we don’t lose any of the detail in the midtones. Perhaps your disappointed because its still not an adjustment layer. Don’t worry because if has that exact functionality with a little workaround. Make your layer a smear object and now apply Shadow Highlight as a Smart Filter. You now have a re-editable Shadow Highlight. This also works for the Variations Adjustment