Change layer content
If you have an adjustment layer and you’ve spent some time painting on the layer mask, the last thing you want to do is start all over again if you decide you should have used a different adjustment layer. Instead, go to the Layer menu and from the Change Layer Content submenu, choose the adjustment layer you want to use. The adjustment layer will change, but the layer mask will be preserved.
i can’t seem to find that option in photoshop CS5 (30 day trial).
i can’t find it in cs4 either!
This tutorial has a screen shot with the option so it must be only for older versions (or else they moved it)