Illustrator :: Convert Halftones Into Opacities?

Is there a quick and easy way to convert halftones into opacities?
 
For example, if I have an element with a 50% black fill, is there a way (besides manually) to convert to a solid black fill with a 50% opacity? This is, of course, a simplified example. But consider artwork with a large variety of halftones that I would like to be scales of opacity instead. As you can imagine, it would be mindnumbingly tedious to have to adjust manually across the entire artwork.
 
The primary use of this would be in recoloring art containing halftones. If I select a different swatch that I want as the new base color, the entire artwork is recolored at 100%, instead of retaining the appropriate halftones. I know I could use the "Recolor Artwork" method, but it would be much simpler to simply have the halftones set as opacities and be able to select any color that strikes my fancy on the fly from the main color palette.