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The visual design itself is not a major concern as far as ranking, however the underlying code changes can present an issue (or an opportunity) depending on the code quality of both the current and new designs. This guide from SEER covers the essentials you need to be aware of during a redesign: http://www.seerinteractive.com/blog/seo-website-redesign-checklist If you avoid dramatically changing the body content of the page, the URLs, the title tags, and the internal linking structure, those are the most common changes that would produce issues.

Yeah hiding keywords in your page is definitely not cool with Google.  Many people do it by making the text the same color as the background.  No one can see it, unless they highlight the area.  Used to be effective, now it's just spammy and will get you banned.

Thank you, for your help. Andy and Michael