Just Google'd "harm in painting a motorcycle helmet" and these are a couple of the comments that came back from that search...
"Do not paint it or attach decals to it unless you have the go-ahead from the manufacturers. The chemicals used in glues and paints can damage the helmet."
"Never repaint your helmet with paints that are not authorized by the manufacturer."
Remember I'm only the messenger... and if that's the case... especially about the decals... then the majority of us would have helmets that are deteriorating on our heads as I type... myself included.
)

Ride Safe,
Fired00d

Hey D00d... thanks for looking around. I know you're only the messenger, and my comments aren't directed at you.
But frankly, those quotes you found via Google sound like a great big load of legalistic horse crap spewed by fearful manufacturers to me....
an' I ain't buyin' it! I can't believe that a simple coat of paint could "compromise" a helmet's integrity. How
exactly would that happen? if someone on here knows, I'd sure like the info. Hell, the helmet ITSELF is painted, right? I just don't get it... what's
different about a helmet shell from say... an ABS or fiberglass saddlebag, fairing, etc? Sounds
very fishy to me that a coat of paint could cause any damage to a helmet... just sayin'... but I'll be happy to stand corrected if anyone has reliable info about this subject...