What are the files which make Counter Strike original?

I know it may sound odd. I have an original copy of counter strike in my steam. But I like a non steam mod of cs . I intend to copy over original files. So which files I shouldnt replace to keep it original steam game?

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An original copy of 1.6 in steam? I think you mean source, because 1.6 is a mod for half-life, not a commercial game. –  Kevin Mar 22 '13 at 7:03
my bad, removed 1.6. It is not source either. just Counter Strike store.steampowered.com/app/10 –  emmett Mar 22 '13 at 7:29
@Kevin CS1.6 is standalone, it was the 1.5 that was the mod –  Lyrion Mar 22 '13 at 10:33