So for example, I have a series of head morphs. I don't want them to be changed as the scene develops. I don't see a feature to lock individual morphs. Is there a way to do this ?

You can go into the settings of the morph and set the limits to match whatever you value you want. That will lock the dial.

There is a way to edit the morph injection file so that it always loads at a specific setting and can't be changed, but I don't remember how to do that.

If don't have access to the "Force limits" option, something you can use with min limit = max limit = value, you have another way it to avoid any move: just enter a very, very low sensitivity, something like 1e-10:

Thank you ! Makes sense.