RSS Feeds

I see there are a lot of plugins for importing RSS feeds, but I haven’t seen any that allow you manipulate the feed coming from our sites. I had a WordPress.com site that was syndicated on another site, so I just gave the sitename.wordpress.com/feed URL to that site’s administrator. Now that I have my own site, I still want that content to be syndicated to that site, but I have other content on my site that wouldn’t be appropriate for that site. Is there a plugin that will allow me to specify which content will be displayed in an RSS feed? Say…by category perhaps? Or, is this even possible?