The baking script works on any current actor, not just hair.  The script alters sets the base shape of an actor to match the deformed shape of that actor at the time the script is run.  So if you take M4's head, make him smile, then run the script on the head, you'll get a head that can only stop smiling if you set the smile morph to -1.0.

When used on dynamic hair, it does seem that there can be some complications, but these lie not with the script but with some oddity in how Poser handles dynamic hair.  As far as I can tell, any script which processes hair will do this.  If the hair or its parent (skullcap) have any transforms applied, the hair will seemingly jump to its default worldspace position rather than its default localspace position (relative to its parent).  That's my only guess for the described error.  The workaround would seem to be to avoid running any scripts on dynamic hair which is not in its default position.  Zero all the transforms on the hair and its skullcap and all actors all the way up the actor chain until the hair is where it would be if its skullcap were not parented to anything.

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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.