Update posts using knit2wp
As you've alluded to, the RWordPress package in R does not support editing of posts. RWordPress uses the XML-RPC interface to interface with Wordpress however, so you'd need to either:
- Find another R package that does allow editing
- Extend RWordPress to support the wp.editPost XML-RPC method. This was only added in WP 3.4 which was released in June 2012. RWordPress was last update August 2012 so it doesn't surprise me that it doesn't support it yet - perhaps the package has been abandoned?
You can read more about the WordPress XML-RPC methods in the WordPress Codex: http://codex.wordpress.org/XML-RPC_WordPress_API/Posts#wp.editPost