One problem with using this method might be the same as weapons in RTW. I experimented alot with making unit's put primary weapons on their back while using secondary.

Still this wasn't possible due to the limitations to the bones bones you could weight the meshes to. If the same limitations apply to these parts, you won't be able to weight a helmetpart to any other bone then the head.

However the possibilitys with creative alphaing still opens for a huge ammount of variety using complex meshes, and alpha. Im rtw i managed to make a horsemodel witch, by only using alpha apeared to be 10 diffrent models.

-Skel-