http://intrcxv4fa72e5ovler5dpfwsiyuo34tkcwfy5snzstxkhec75okowqd.onion/blog/sfeed
As you might have gathered, sfeed_update sources your sfeedrc, and this means you can override all of its functions. For example, filter is a function that takes the feed name and URL, and the feed data is piped to it. This means you can declare the filter function in your sfeedrc to run every feed through a filter before it's saved.