Relationship query is passed to metadata query, so you can use all metadata options in the relationship ege*

Do you use icondirect.php for it?

$tmp = new ElggFile();
$tmp->owner_guid = $user->guid;
$tmp->setFilaname("tmp/upload.jpg");
$tmp->open('write');
$tmp->write(file_get_contents($photo_url));
$tmp->close();

$user->saveIconFromElggFile($tmp);

$tmp->delete();

if i launch a lightbox that contains comments, will hypeinteractions still work in the lightbox?

It should

ok, thanks - there are reasons why i am not using hypeInteractions - but i don't recall exactly why now.. i will look at it again soon.