Duplicate website and change a little

After this last google spam update I have seen a lot of threads about lose in traffic. I wanna ask this question, if we have a site that was performing well but had many posts, is it possible to totally copy that and change few thing into a new domain? If its possible and will work is it better to copy directly from ftp and database or should we use a plugin to duplicate it?
Thank you

You should do a 301 redirect
c/p is plagiarism if they're already indexed