2 seperate feeds updating the same set of nodes (feeds module)
EDIT: there's a patch in this thread: https://www.drupal.org/node/1539224

I knocked something together that allows my second feed to update the nodes from my first feed. Not sure if this is the right way of doing things but it works. Here's what I did in case it helps someone else in future:


Created a custom processor that extends FeedsNodeProcessor
Copied across all of FeedsNodeProcessor's functions to the new class.
Overrided the existingEntityId function as follows (harvard_format is my secondary feed and pure_feed is my primary feed):


protected function existingEntityId(FeedsSource $source, FeedsParserResult $result) {

if($source-&gt;id == 'harvard_format') {

  $query = db_select('feeds_item')
    -&gt;fields('feeds_item', array('entity_id'))
    -&gt;condition('feed_nid', $source-&gt;feed_nid)
    -&gt;condition('entity_type', $this-&gt;entityType())
    -&gt;condition('id', 'pure_feed');

  // Iterate through all unique targets and test whether they do already
  // exist in the database.
  foreach ($this-&gt;uniqueTargets($source, $result) as $target =&gt; $value) {
    switch ($target) {
      case 'url':
        $entity_id = $query-&gt;condition('url', $value)-&gt;execute()-&gt;fetchField();
        break;
      case 'guid':
        $entity_id = $query-&gt;condition('guid', $value)-&gt;execute()-&gt;fetchField();
        break;
    }
    if (isset($entity_id)) {
      // Return with the content id found.
      return $entity_id;
    }
  }
  return 0;
}
elseif ($nid = parent::existingEntityId($source, $result)) {
  return $nid;
} else {

  // Iterate through all unique targets and test whether they do already
  // exist in the database.
  foreach ($this-&gt;uniqueTargets($source, $result) as $target =&gt; $value) {
    switch ($target) {
      case 'nid':
        $nid = db_query("SELECT nid FROM {node} WHERE nid = :nid", array(':nid' =&gt; $value))-&gt;fetchField();
        break;
      case 'title':
        $nid = db_query("SELECT nid FROM {node} WHERE title = :title AND type = :type", array(':title' =&gt; $value, ':type' =&gt; $this-&gt;config['content_type']))-&gt;fetchField();
        break;
      case 'feeds_source':
        if ($id = feeds_get_importer_id($this-&gt;config['content_type'])) {
          $nid = db_query("SELECT fs.feed_nid FROM {node} n JOIN {feeds_source} fs ON n.nid = fs.feed_nid WHERE fs.id = :id AND fs.source = :source", array(':id' =&gt; $id, ':source' =&gt; $value))-&gt;fetchField();
        }
        break;
    }
    if ($nid) {
      // Return with the first nid found.
      return $nid;
    }
  }
  return 0;
}


}   


Copied across the the Process and newItemInfo functions from FeedsProcessor.
Overrided newItemInfo as follows:


protected function newItemInfo($entity, $feed_nid, $hash = '') {

$entity-&gt;feeds_item = new stdClass();
$entity-&gt;feeds_item-&gt;entity_id = 0;
$entity-&gt;feeds_item-&gt;entity_type = $this-&gt;entityType();
// Specify the feed id, otherwise pure_feed's entries in the feeds_item table will be changed to harvard_format
$entity-&gt;feeds_item-&gt;id = ($this-&gt;id == "harvard_format") ? "pure_feed" : $this-&gt;id; 
$entity-&gt;feeds_item-&gt;feed_nid = $feed_nid;
$entity-&gt;feeds_item-&gt;imported = REQUEST_TIME;
$entity-&gt;feeds_item-&gt;hash = $hash;
$entity-&gt;feeds_item-&gt;url = '';
$entity-&gt;feeds_item-&gt;guid = '';


}