Mostly i want to use Inkscape for GUI design and for drawing small icons. Love the Icon preview

Having read a lot of good tutorials on how to archive some effects one thing has puzzled me from the beginning.
Example:
I draw a rectangle and apply a "drop shadow" effect using the filter editor as described in this tutorial.
The shadow is too dark, i need to lower the opacity of the effect.
Question:
How can i change the opacity of the effects only?
My workaround was to duplicate the layer ( no sublayers in Inkscape , meh) , apply the effect to the duplicate layer and then lower the opacity of the duplicate.
Is there another way to go? Or can the workaround be automatized ( copy layer --> apply effect to duplicate --> lower opacity of duplicate) ?
Thanks for your input
