I just want to retexture the leather cuirass with the saviours hide texture. How do I do this and can it be done in the CS

It can be a pretty involved process. http://cs.elderscrolls.com/constwiki/index.php/Category:Texturing_Tutorials's a list of the Texturing Tutorials at the CS Wiki. This is a very basic one http://cs.elderscrolls.com/constwiki/index.php/Texture_Replacer/Tutorial, and might serve your needs. Good luck!