Shape keys: Reset part of the model or only use specific faces possible? I am currently trying to apply shape keys to a high poly model, which has got a mirror edge, but that modifier has been applied to properly apply textures on its surface.  Somehow, due to little differences on the x-axis, I got a kind of unexpected result as I copied a shape key from a topologicial mirrored shape key.  In this, I only want parts of the horse's mouth to change so that it can take the bit of its bridle properly. I don't need the rest of the unwanted changes. Is there any way I can reset or unshow those parts of the shape key results that I don't want (don't affect all the object's faces by the shape key)? If there is anyone out there having figured out a solution, who might tell me, I'd be very happy for the help.
Pictures for explaination below.
 (Basic mesh)
Enter edit mode through the broken shape key, select vertecies that you do not want to affect your basic mesh and then press 'space' and search "Blend from shape" press 'enter
Then press T and on the left you should see options down at the bottom
1-select basis (your basic shape key)
2- Blend 1
3 Turn off Add