Quote - @Cage: The channel to look for is JCM-MouthOpen in the BODY actor. I regard the mouth open morph as a JCM, and all my JCMs have a master channel in the BODY. The master channel is slaved to the original rotation, and all the channels in the body parts are slaved to the master channel. I did that specifically to allow users and developers easy control over the workings of the JCMs. I think you can also twiddle the master channels by hand and see what happens. They are not hidden, just stowed away in collapsed groups.
But personally, I would just subtract the default MouthOpen from whatever new shape I was making and store the difference as a new morph. That should make things less complex to set up, and with any luck, the new morph might then even be useful when the mouth is not open.

I do like the way the JCMs are set up.  This one seems a bit trickier than the others, because the morph moves with the jaw and the jaw moves with the morph.  A simple deactivation switch doesn't seem to be something I can implement easily.  I don't want to screw up the ERC flow, just be able to block it selectively.  I think I'm going to add a second XROT dial for the jaw, so I can use it with other mouth morphs if wanted.  I think that should be possible.

I'm also going to try linking the translation dials for the teeth and eyes to valueParms in BODY.  I'm finding that some faces really require moving either the teeth or eyes, or both, and the translations end up in poses, which causes trouble.  Linking them to valueParms should prevent that trouble.

I agree with your thinking about the MouthOpen morph, for new morphs being created.  I have some I've been using and I want to be able to keep using them, at least to some extent, until I learn to use the default expressions effectively.

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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.