Does site's layout change harm Google ranking?

Is it possible to harm ranking and pr with total layout change?

[GreenLeaf]

Hi All!
Is it possible to harm site's ranking and PR with total change of site's layout?
The content is the same, the colors are the same, the design looks very similar to the old one, but the layout is entirely different to do the site to be more SE friendly (text is closer to the beginning of the page).
Thanks in advance.

[takagi]

PageRank
No change for PR if the linking structure is not changed, and the size of the page (HTML source file) stays below 101k. The only exception I can think of, would be a penalty for things like text on background with (almost) the same color.

Ranking
Ranking can be influenced by changing the layout. Words at the start of the page could be more important to Google. Changing links from images to text might help your ranking if the link text contains keyword(s).

[GreenLeaf]

Thanks!
As far as i understand it's Ok to do this.
And if i'll also change server parsing mode (in htaccess) from shtml as html to php as html?

[takagi]

Changing URLs (by changing the extension from 'php' to 'html') will result in a temporarily drop in the PR of some pages if the PageRank is recalculated with some pages not yet known spidered with the new name. But that should be solved in time unless you have some deep links (links from other sites to pages on your site) to no longer existing pages without a redirect (301 - Moved Permanently). Adding the 301's for all pages will make the transition smoother and will also help for user of Search Engines that are not as quick as Google to update the index.

[GreenLeaf]

Thank you very much, Takagi!
A far as i understand, all must be Ok if i don't change link structure and page extentions.