What you're describing is basically a gain control within the eq, but with differences. The eq would have to intelligently re-map a new set of filters to do that. For example a simple high shelf boost of 3dB brought down 1dB would intelligently need to convert that to a 1dB low shelf cut with a 2dB high shelf gain. The thing is, you might not be able to recreate the same opposite curve exactly with more complex filters, but I may be wrong. I do get what you're asking, but I can't imagine many designers going through the effort of doing that. It is an interesting concept. My guess is anything out there would simply just use a gain change instead of an intelligent algorithm (which probably wouldn't actually be too hard to engineer) which defeats the whole purpose of cutting only. It really complicates the eq design.

I wonder though. A simple peak at 1khz uses one filter. To invert that, you'd now need TWO filters to achieve the same result. Do the total artifacts add up to be the same in the end or even worse? I'm curious.

I must do some cut vs boost experiments...

What you're describing is basically a gain control within the eq, but with differences. The eq would have to intelligently re-map a new set of filters to do that. For example a simple high shelf boost of 3dB brought down 1dB would intelligently need to convert that to a 1dB low shelf cut with a 2dB high shelf gain. The thing is, you might not be able to recreate the same opposite curve exactly with more complex filters, but I may be wrong. I do get what you're asking, but I can't imagine many designers going through the effort of doing that. It is an interesting concept. My guess is anything out there would simply just use a gain change instead of an intelligent algorithm (which probably wouldn't actually be too hard to engineer) which defeats the whole purpose of cutting only. It really complicates the eq design.

I wonder though. A simple peak at 1khz uses one filter. To invert that, you'd now need TWO filters to achieve the same result. Do the total artifacts add up to be the same in the end or even worse? I'm curious.

I must do some cut vs boost experiments...

Although its not what you are looking for you may want to try GlissEQ from Voxengo. 

There is a free plugin set from ReaPlugs 
 
http://www.reaper.fm/reaplugs/
 
the function you mentioned is within ReaFir it is not in the default ReaEQ. From within ReaFir, select from the MODE SECTION.
 
You can double click on the curve to add points and when done you may hold "CTRL" to move the entire curve up or down.
 
hope this helps... cheers!!!

Yes but that will simply be a gain change, not reconstructing the filters to create an identical response. Different process. Wether the sound is any different between the two is another matter. But in some eqs it may well be - especially in ones modeling analogue.