Ive just finished my first head rig with blend shapes, and realised that I didnt freeze transformations for the jaw

So the jaw is stuck at 20º, and when I put the input of the blend shapes under the skin cluster it moves the blend shape jaw 20º upwards. I hope I have explained this clearly enough.

So is there any way I can freeze transformations of the jaw joint even though it is connected to a million different things, and if not what do I do?

*And also if I use two blend shapes at the same time the jaw will go up twice as much