I’ve not seen any good way to touch that up. I’ve got a GS with the black chrome grille and it’s got the typical rock chips and dings from being a daily driven car for the last 8 years. If I ever get the bumper cover repainted I’ll probably just replace the grille. They’re not too terribly expensive on eBay. I’ve seen them on RockAuto for $259 depending on which “level” you choose from their vendors.