since I have personally refinished 1 nose and two rear bumpers, I would recommend you try to find a better skin.
but if thats not an option you can sand down the area until the lines are all but gone, then the skin can be repaired with dominion or comparable flexible bumper repair compound, its 2 part.
then it can be covered with epoxy primer.
then spot areas with polyester 2 part finishing putty
then some sandable primer very thin
scuff and paint.
the epoxy primer is essential to your bumpers finish