Ok guys, I figured out how to do it.

Is easier than it looks like. The problem is me, the clumsiest clumsy of all clumsies (I don't know how this will read since I'm using Google translate).

The thing is, (I'm blind), in the materials panel, on the top right is a "Materials" tab with a drop down list. When you open it you find the different anatomical parts affected by the material that allows you to assign and parameterize all the aspects of each of them independently :).

Well then you have to select each anatomical part one by one and in the EZBlinn panel give the refraction value you want. Since I didn't want reflections, I set them to zero. I only applied the mod to SkinHead (Head and Neck), SkinTorso (Torso, Abdomen and Hips) and Skinlimbs which fully affects the arm, hands and legs. For the rest, eyes, lips, teeth, nails, I left them as is. Good for Poser13, I love this interface design. You just have to dedicate a little time and the great help that my fellow forum members have given me to understand the material interface. Thanks and a hug to everyone. Signed: The clumsiest guy of all the clumsy guys.