I have heard of people removing the lenses and sanding them with 2000 grit paper then polishing them clear, but that would destroy the optical dispersion pattern of the ridges and probably make the headlights much less effective.
Yellow tint? Which lights are you talking about? The yellow side markers? If so, there are clear replacements available lots of places. If your headlights are yellowing, then you can get some plastic polish and bring them back.