I don't think a silver-coloured Sharpie will cut'it, so to speak! May be get a custom vinyl shop to spec & cut some self-adhesive metallic overlay pieces to affix to the non-Sports grille pegs...
You got a pheasant in your grille? That must be an interesting story.I'm sure Mercedes will sell you a shiny diamond grille. If it gets totalled by a deer and or pheasant, as is the case with me... you'll want to buy a new one. Merc must be ready for this eventuality.
Leave the marker pens to the artists!