For a situation like the seam along the center of the body, I highly recommend storing a Morph target, applying the scales you want manually along there, then using the Morph brush to revert any problem areas. You can also use layers to do it even more non destructively.
I followed your video and did the masking as you did, but in my case my character did not changed. The noise affected the hole character with mask or without it why is that?