As you know, layer styles are very handy - at any time you can re-open style settings and update them.
In the meantime, you can't edit styles in the "regular" way. For example, how about erasing unnecessary shadow area?
- In the Layers palette, select a layer with the "fx" mark.
- Open the "Layers" dialog and double-click the "Layer from Style" (Layer from Style).
Now the layer style appears in the palette as a separate layer named like "Effects for <source layer's name>" (screenshot).
Keep in mind though that the style settings are not editable any more. Also, you can't convert the "Effect Layer" back to a layer style.