Make small changes to a finished mask, without altering the rest of the tracked mask? (pen tool)

I have a mask of a person's face (profile) while speaking.  (I used the pen tool to create the mask)

The mask is complete (lots of small movements, head turns, etc....) and when I make small adjustments to the mask, and start clicking the track button, frame by frame:

Problem is, the other parts of the mask start moving in the wrong directions.  Slighty moving, but enough to ruin my prior work.

Is there a way to lock in a finished mask, so no lines move from original tracking.... and make small changes to one little segment?

The regular 'lock mask' will lock the whole mask.  I hope there is a way to make a change on one section without damaging the rest of the tracked mask?  OR must always start from scratch and do the whole mask over again from the begining for a simple adjustment?

Thanks for reading and your advice.

Best,

Letty