Pre-facelift parts won't fit, The headlamps are a different shape, the bonnets different too. I'm hoping the facelift Zetec S has a similar to current grill layout, then it would be an easy swap. If Ford don't do it, I will...If I ever get my hands on one.
I prefer the street-pack alloys to the ST ones too.
Actually, modifying the front of an ST to look like a pre-facelift would be relatively easy. The front wings are the same on both models. Therefore, only the ST front bumper, headlights, bonnet and grilles would have to be replaced with pre-facelift items. They will be a straight swap as the mounting points will be the same.