I have some pages on my site that are plain HTML pages, but I want to add some ASP .NET type functionality to these pages. My concern is that if I simple rename the .html page to .aspx that I will break links, and lose SEO, and so on.
I would think there is a ‘best practice’ for how to handle this situation.
Create your new pages on aspx, and just serve 301 permanent redirects from the HTML pages.
Search spiders are smart enough to realize the content has moved and will not penalize you.
Both Google and Yahoo also say that they parse a meta-refresh with no delay as a 301 redirect, so just do something like this: