Alright, here's the new script - in fact, it's three scripts in one.
http://www.fileden.com/files/2010/2/7/2 ... minance.pyIt installs 3 menu options to a submenu "Luminance" under Filters. I'll go through them briefly...
"Remove" simply removes all luminance information from a layer, leaving only the chroma. In other words, it sets the luminance of a layer 50% on the whole layer.
"Extract" extracts the luminance into a new layer, or in other words: it separates a layer to luminance and chroma. The luminance layer is automatically set on grain merge, so the result should be identical to the previous layer.
And finally...
"Hue-Saturation" - this uses the earlier two scripts internally to the effect of allowing you to adjust the hue and saturation of a layer while preserving the luminance of it intact.
I might be writing a more advanced version of the hue-saturation script, if I have time some day... for now, if you want a better interface, simply use the Extract to extract the luminance, adjust the chroma layer with the native hsl tool, then remove luminance from it, and merge the luminance down. (as that is basically what the hue/sat script does...)