Alright, so before I get started I am going to mention that this HOWTO is being done on the BS captain cardinal helmet. If you are reading this from the future and BS has a standard FO helmet on shelves, I would assume that this HOWTO would still apply, assuming it uses the same molds/form as the captain cardinal helmet.
EDIT: There is now a white version of the hasbro helmet. It does use the same molds, and this howto will still be an accurate guide on how to modify it.