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If you currently hold a good ranking, the keywords and the description should stay the same......actually, in most cases the keywords and description should only change when the content or the topic of the site changes.
What you can always tweak is the little things inside the site and the content. Try some new things within the HTML coding to find out what works, or try various keyword densities.......there are many things that you can do if you are not satisfied with your current listing.