i recommend you first make a back-up from the helmet you want to replace. give my files the same name as the files you want to replace and put my files in the right folder

rbctt.nif    >  CM_Meshes\Equipment\Helmets
rbctt_d.dds  >  CM_Textures\Equipment\Helmets
rbctt_n.dds  >  CM_Textures\Equipment\Helmets
rbctt_s.dds  >  CM_Textures\Equipment\Helmets