Well the helmet u speak of actually isnt in the default rc game. Its been modded
I know the process of how theyve done it but not where theyve got the helmet mesh from,
I guess u could download the arctrooper mod and have a look inside at various texture and staticmesh pakages. there you will find the helmet mesh and also the texture for it,
Trouble is the way the mod has been constructed it overwrites existing default pakages,
what i would suggest is to find the static mesh for the helmet place it on a map then save it to your own new staticmesh pakage and also create a new texture pakage Duplicate an existing shader and rename it and save to your new texture pakage and same for the helmet texture.
if u open the shader properties you can manually edit the paths to your helmet texture. and in your new staticmesh pakage change the shader for it,
This process will require you to expand your knowledge base ,there's no "kwik fix" like poping down to shops for a dvd.
The animation set used is clonetrooper no helmet and where the texture /shader for the clobne head is has been supplanted by the invisible texture then a cteffect has been made in which is the staticmesh of the helmet so you would need by trial and error to position the helmet mesh to correct ATTACH position on the shoulders.,.etc etc