Magnets. Move the magnet relative to the base to deform the target geometry. I know, magnets are counter-intuitive at times. Took me two years to learn them. Now I use them constantly. :) If the region is pre-grouped, you should be able to just go ahead and invert the polygons. The invert button you mention inverts your group selection. The invert normals button is down near the bottom of the Grouping Tool box/window/popup thingie. Umm. I don't have Poser in front of me, so I can't give you the specific terms, but look for the word "normals".... Anim8or is actually a very good idea. I need to brush up on it, myself, instead of fighting with RDS so much. :)

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Cage can be an opinionated jerk who posts without thinking.  He apologizes for this.  He's honestly not trying to be a turkeyhead.

Cage had some freebies, compatible with Poser 11 and below.  His Python scripts were saved at archive.org, along with the rest of the Morphography site, where they were hosted.