Interesting.  I don't think there's any way to 'lock' vertices...

A couple of vaguely related things that may or may not lead to an answer:

Sometimes Poser doesn't quite know how to find an attached prop
like a hair prop.  It can be hard to reach such things in Python, and
sometimes they don't appear on the selection menus.

Also, are you sure the zone is really where you want it?
Have you looked at it from two different angles to check that
it's not really out in front of the hair?

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