Setting field values on a per-import basis when using Feeds
There's also hook_feeds_after_parse() which lets you modify what's being saved to to your targets.  Something like this should work:

function my_module_feeds_after_parse(FeedsSource $source, FeedsParserResult $result) {

  if($result-&gt;title == 'title-of-feed-importer') {
    foreach($result-&gt;items as $item_key =&gt; &amp;$item) {
      if ($item_key == "name-of-the-field") {
        $item = 'Value to set';
      }
    }
  }

}