customising custom field format

Hi basically i need to override the code below in funcitons php

/**
 * Display list of post custom fields.
 *
 * @internal This will probably change at some point...
 * @since 1.2.0
 * @uses apply_filters() Calls 'the_meta_key' on list item HTML content, with key and value as separate parameters.
 */
function the_meta() {
	if ( $keys = get_post_custom_keys() ) {
		echo "<ul class='post-meta'>\n";
		foreach ( (array) $keys as $key ) {
			$keyt = trim($key);
			if ( is_protected_meta( $keyt, 'post' ) )
				continue;
			$values = array_map('trim', get_post_custom_values($key));
			$value = implode($values,', ');
			echo apply_filters('the_meta_key', "<li><span class='post-meta-key'>$key:</span> $value</li>\n", $key, $value);
		}
		echo "</ul>\n";
	}
}

i know it involves add_filter or something but when i do this:

add_filter('the_meta_key', 'modified_meta_matt', $priority = 1, $accepted_args = 1 ); 

function modified_meta_matt() {
	if ( $keys = get_post_custom_keys() ) {
		echo "<ul class='post-meta'>\n";
		foreach ( (array) $keys as $key ) {
			$keyt = trim($key);
			if ( is_protected_meta( $keyt, 'post' ) )
				continue;
			$values = array_map('trim', get_post_custom_values($key));
			$value = implode($values,', ');
			echo apply_filters('modified_meta_matt', "<li><span class='post-meta-key-3'>$key:</span> $value</li>\n", $key, $value);
		}
		echo "</ul>\n";
	}
}

?>

It does work, but it displays the custom fields repeated like 6 times!
thanks for your help!