Dataflow Profiles – Import and Export Errors in Magento

You can't just add arbitrary attributes in the XML declaration; there has to be PHP which processes them. You need to rewrite the Mage_Dataflow_Model_Convert_Parser_Csv::getCsvString() method to evaluate it. The core method looks like this:

/**
 * Retrieve csv string from array
 *
 * @param array $fields
 * @return sting
 */
public function getCsvString($fields = array()) {
    $delimiter  = $this->getVar('delimiter', ',');
    $enclosure  = $this->getVar('enclose', '');
    $escapeChar = $this->getVar('escape', '\\');

    if ($delimiter == '\t') {
        $delimiter = "\t";
    }

    $str = '';

    foreach ($fields as $value) {
        if (strpos($value, $delimiter) !== false ||
            empty($enclosure) ||
            strpos($value, $enclosure) !== false ||
            strpos($value, "\n") !== false ||
            strpos($value, "\r") !== false ||
            strpos($value, "\t") !== false ||
            strpos($value, ' ') !== false) {
            $str2 = $enclosure;
            $escaped = 0;
            $len = strlen($value);
            for ($i=0;$i<$len;$i++) {
                if ($value[$i] == $escapeChar) {
                    $escaped = 1;
                } else if (!$escaped && $value[$i] == $enclosure) {
                    $str2 .= $enclosure;
                } else {
                    $escaped = 0;
                }
                    $str2 .= $value[$i];
            }
            $str2 .= $enclosure;
            $str .= $str2.$delimiter;
        } else {
            $str .= $enclosure.$value.$enclosure.$delimiter;
        }
    }
    return substr($str, 0, -1) . "\n";
}

As of CE 1.9.0.1, only four product types can be imported using ImportExport:

• Simple
• Configurable
• Virtual
• Grouped

These types and their import models are defined in the ImportExport config file.

I'm afraid you would have to write your own import adapter for downloadable products.