- SiteUrls_override.config is considered invalid and should be removed from a 9.0 site.
- Any URLs previously defined using a SiteUrls_override.config file should be converted to use one of the appropriate new plugin types.
- Users can no longer override existing core URLs.
- The majority of core URLs are now extensionless - meaning they no longer contain the .aspx suffix. However for the sake of backward compatibility, most extension-based urls will redirect permanently to the equivalent extensionless version. In turn, this means that any IIS-level rewrites used in older versions to accomplish the redirect should be removed.