So glad I found this thread. Started modifying my Hasbro helmet this morning. You are right- lots of hidden screws, but with patience, I had it apart in no time. Egon asked about those covers on the screws on the earpieces- I took a utility knife and (very carefully) pressed into into the screw cover, making an "X" cut. Then I took a little screwdriver, shoved it into the "X" and with a twisting motion, got the covers to pop out. (did that make any sense?) I guess u could just use a small drill bit to drill into them as well.
Joshsurf- I'm curious what you used for your visor?