I want to update a site by changing the WP theme. This, of course, may mean changing the names of categories to seam well with the theme. Will this screw up my rankings?
If any of your urls are changing, this could have a negative effect on your rankings. Ideally you would setup 301 redirects from any url that is being changed to the new url. That would limit any negative effects. Any negative effects would likely just be temporary. In time the search engines will reindex all of your pages and restore your rankings. It may also help to submit a new sitemap to Google Webmaster Tools after you do this. Another thing that may help is to build more backlinkk and add more content after changing your theme.
Why would a change in theme require you to change your category name? As Vansterdam said, use a 301 redirect if you have to change it.
exactly! people change theme all the time which doesn't have anything to do with category change. its just the layout you are changing which doesn't require you to change the content or categories.
I'd probably change the categories because it would look messy with multiple words as it has now. It's a magazine style I'm thinking of changing to, and the categories are across the top. With 2-5 word phrases, all different lengths, it would not be symmetrical and just look messy. Know what I mean?
you can change you theme without changing anthing else however changing your theme may impact your ranking as eac theme has differing structures such as a h3 for the title in the sidebar or having the header logo as a h1 on each page, you need to ensure your theme is seo optimised and then it will not impact your ranking at wp.org/extend/themes search for seo or seo friendly themes, these are generally better wrt to SEO but they still have some flaws
I agree with the others, changing a theme is one thing, it's tried and acceptable. Renaming categories and messing around in that department might set you back a lot. Googlebot is a program, don't confuse it.
well if you are changing your any of your URL then it will surely effect...the other thing when you will changing the website theme and all then there will be some down time ....in this time period if crawler visits you then there will be sure effect on your ranking...