Does frequent changes to a website like changing the page extension, internal links, external links, content, design, etc. affect the search engine rankings?
Yes most things that you do to your website will affect search engine rankings. The more frequently you write content for your site the better as this allows Google to crawl your site and update it. Changing page extensions would also affect your search engines but most probably in a negative way at least at first. Hope this helps.
I notice that changing the title of your site can hurt your PR and SERP. Changing template can also be detrimental to your site.
Changing page extension and links (internal and external) can have a big effect. If you change page extension, 301 direct the old URL to the new if possible. Adding new pages and linking those in is a good thing to do.
As to templates they are just a HUGE negative Dynamically changing sites are a positive - look at CNN.COM PR 10.0 - an easy example
Frequent changes might affect negatively your SERP so don't exaggerate. Not to be mistaken with publishing new content which is good obviously.
Changing the extension of your webpages frequently can definitely affect you ranks negatively since the spider has crawl after each change to get them listed properly. Changing content and internal structure can be good or bad depending upon the exact changes you make. Changing title and description frequently is not a good idea.
its not about changing the template that affects SERP.if you change the look of the website completely but yet kept the links intact it wouldnt affect you.The look and backend of the sites are different as far as the bots are concerned.
I think changing title may HELP or HURT you SERP.. It's 50/50... depending on what keywords you have used...
I wouldnt get too worried anyone who is considering a total redesign. I totally changed my website about 2 months ago like as much as you could. I went from having a html/css/php coded site that I had to edit manually with 100 articles and overall about 120 pages to redirecting EVERY url and changing the site to a unique wordpress design that I had coded and obviously moving to WP. Yes there were significant changes in the traffic for a couple of months but it has gone back to normal now