Forum Moderators: Robert Charlton & goodroi
if you do not change the URLs but only design/layout, why shall it have any influence?
On-page factors (keywords and density, amount of text, etc) are very important in where the page is placing now. If these are changed for the worse, it could drop in the results.
Zardoz, the meta tags count for very little and are mostly ignored by the search engines. The <title></title> is the most important part of the header. Be very circumspect about how it is changed. Other than that, your keywords in the text itself are the big thing. Don't turn them into spam by loading the page with them, but make sure you have a good occurence (with variations like plurals) that appear in a natural fashion on the page. Feel free to make the page nice and "fat" with lots of content - the SE's love text, that's their main diet.
I play around with my homepage a lot and it never seems to make a difference. I think it's because off page factors are a bigger part of the algo.