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If the keywords placed in your keywords tag aren't used on the page there is no reason to have them in the tag.
Keyword tags are largely ignored by the search engines but if you decide to use the keyword tag keep it focused on the page content, not the entire scope of the site.
Some directories and search engines may refuse your site or a specific page if you overdo it.
Most engines don't use the keywords tag at all or only the words that also appear on the page.
Just to add, that Now-a-days, Meta keywords are loosing their importance with search engines specially with Google. So, Give prime importance to <title>, meta description, <H1> tag, text links etc. rather than focusing on Meta keywords. They add to page-size but are less important as per the search engines are concerned.
Regards
Guddu