1. I am not an expert and you should make sure what you do with your helmet is safe.
2. Do not modify some of your helmet safety aspects too much like : straps, outer shell, padding, etc. Unless someone who knows exactly what they are talking about says its safe.
3. A helmet is a helmet, if a skateboard helmet can do the job to protect on pavement, it should be fine for skiing.
I see a lot of people on the mountain who don't clip their helmet straps or don't have any at all. Doing so decreases the protection factor of your helmet big time. Ex. You fall on a steep run with rocks around your helmet might fly off as you tumble. Then as you're tumbling you could strike a rock and crack, you're dead. With a helmet that might be a concussion. (This is a made up example from the top of my head, but it's only one of many possible things).
I also know a lot of people wear skateboard helmets and because they aren't warm they wear a tuque underneath. I know people who take out their cushioning pads to make room for the tuque. Don't. Why? Because those pads do exactly as their name says: cushion and pad. That said, you can find someone who can fit you with some thinner ones at some shops. Find someone who knows.
My mom works for Whistler Blackcomb and on powder days while I come home with a big grin, she comes home with stories of all the injuries that day. Including "Heli Evact's". Because it's powder, people thinks it's "harmless" and go big. Injuries are up to 3x as bad and as common on powder days. I know I've considered not wearing my helmet in the soft snow but just because the snow is softer, doesn't mean that trees and rocks won't be there.
