I don't have a choice! 
I have a fiberglass helmet which was already painted by the maker and I am in the process of rear mounting a visor to it with minimal damage to the paint. So far I have the rough shape cut out with no damage, so now starts the sanding work. FB helmets are harder than I thought...The visor area is thick and the dust get everywhere!!!!! lol
I do think it's easier to install the visor before the paintjob, just in case there is damage. I just don't have a choice, lol
