I would say that you should check with your GML before you go forward with full helmet idea.
Personally I don't see a problem with it due to the following reasons.
1 - The CRL is still listed as WIP. I'd say that opens for some leeway.
2 - Mask is a somewhat ambiguous term and the CRL reads:
I'd say that, in it self, would give you the option of doing a full mask/helmet.
3 - Concerning the hood the CRL states:
Meaning that technically you could have a Hello Kitty back to your mask because it shouldn't be visible anyway.
Considering that a mask/helmet that would sit so snuggly on your face I'm sure you would want to keep the back open because of the heat. Only time and experience will tell though.
If you really want a full head mask/helmet I'd suggest you make it two-piece (as per #1 above) so you could decide to go without the back on warmer days or when the event is formal and the hood should be up all times (as per #3 above).