How do I use select verts when I use relax/soften in the deformation corrector?
You are right, the Relax/soften brush in the Ribbon does not respect selected vertices only and performs the operation on the whole mesh regardless of the selected verts. However, the Paint deformation tool in the Paint Deformation rollout of the Edit poly/Editable Poly does act only on the selected vertices. You can relax the verts with the relax option and Use push/pull on the selected verts as well. The relax brush here is not nearly as strong as the effect you see with the Brush on the ribbon, so you will have to paint it multiple times to get more movement, but depending on your needs it may work for you.
Also make sure you remember to hit "Commit" button when using the Paint Deformation tool in the Editable poly rollout or you may lose all your changes if you switch to the move tool or select another object in the scene without doing so.
You can also use the "Constrain to Spline" feature in the ribbon by first drawing a spline on the surface of your mesh to cover the verts you want and then picking that spline and activating the Relax/Soften tool. While this does work, it is a bit of a pain to use and you need to adjust the brush size to get results that track the verts. I think it would be an improvement to add a control for constraining to selected verts in the ribbon like there is in the paint deformation rollout of editable poly.
