Hello, I have a forum which ranks well on Google for a competitive group of keywords. I have no website on my domain, it just takes the viewer to the forum index. The software is phpbb 3. I want to install http://www.phpbb-seo.com/ which is a mod that will change my thread ids from a seo unfriendly format like ..viewtopic.php?f=1&t=152 to "topic=preorder-wrath-of-the-lich-king.html" My question is, is this sort of thing liable to mess up my high ranking if suddently all my threads that Google previously crawled are not found after the patch? The indexed page is http://www.wowforums.com/forum/index.php and will be unmodified. So my index will remain the same, but suddenly 90% of my site's contents will be different when following links from the index. Too long to read summary: If I upgrade my message board and all the thread links all change/break but the index that is highly ranked does not change, will my rank remain the same in google? Huge thanks for any/all responses I appreciate your help!
So, you'll have the same content(old content),..but with "seo friendly url's" which google may consider duplicate content. Also, I heard from most of the people that changing the phpbb urls to phpbb-seo url's can eat lots of memory.
Yes your ranking will be affected. However, your ranking may recover if the old URLs are 301 redirected to the new ones. I personally once installed a same kind of mod for my MYBB forum and it was the worst thing I did. The mod changed the URLs to search engine friendly URLs, but there was some problem that mod created for me. I disabled and enabled the mod few times, everything seemed to be ok, but after few days, I found that google was showing lots of duplicate page titles in webmaster tools. I did some investigation and found that the mod was the culprit. That mod created a problem where the same URL can be accessed by many different URLs. I then disabled that mod. I suggest you do some investigation about that mod before enabling it.
I wouldn't think it would be a good idea to do that since Google already crawls your site often. If you were going to do that, you should have done it right from the start.