What’s the best way to paint the front grill, without removing the clam? Mine has aged and is more grey than black.
Mask off, brush down, spray black?
Best paint to use?
Will over spray be a problem or visible on the crash structure behind?
It’s dead easy on an S1, the grille is removable, just held in with two screws or scrivets 
Sorry I know that probably doesn’t help if you have an S2, but couldn’t resist. 
I know of a few people who have brushed on hammerite or similar to some success. I doubt you’d notice black overspray on the crash structure though
To be honest if your not wanting to remove the front clam brush painting is the only option. Why not spend a hour and remove clam, and properly spray that way you can reach both sides.
Also a good opportunity to see what it is like under clam.