You can unpack the meshes from BSA file. BSA is archive file containing meshes, textures etc. You need BSA unpacker (or similar) for that. CS disk had those files already unpacked iirc.
For changing colour of the helm, you'll need Nifskope, Photoshop or Gimp, and unpacked files that you need.
First open mesh in Nifskope and find out which texture it uses. Then recolour that texture in PS or Gimp and save as. Then, open mesh in Nifskope and change texture to your new one and save as.
Then, you can turn on CS and create new helm.
That is if you want have both original helm and your new one. If you want to replace original, then just recolour texture and save it under same name in your Data FIles\Textures\...\.