Now that you have source material to look at, the foam rear pieces, are put in in such a way, that you could 'cut them out' and be able to add or remove them when you wanted to. So if you couldnt wear the helmet with them in, you could pull them out. The front, you glue atop the gasket, or cut away the gasket depending on how much room you need. The rest of the pieces are in places that dont really effect the size of the helmet. Therefore, if you take your time while mounting them, you should be able to make them easily removable/insertable, thus making it wearable for any head size.
I also put pre-set mounting holes in the rear piece. So you could mount rubber tabs in the helmet, and remove the WHOLE gasket by just poping it out. You would need to stick mount the edge of it, so it doesnt hump up, bit it should work nicely.
Questions comments and concerns beforeI move forward?