OMG, Thank you :=)
i had
$gallery_data = $current_gallery->child( 'template=gallery' );
foreach( $gallery_data->image as $image ) {
$image->tags = "TEST-Tag";
}
$page->save();
$gallery_data->save() did the trick
i have a little problem using this module. everything works fine, i just got the "move" button/function too on pages allowed to edit. Moving does not work anyway but it's a little bit confusing that the button appears. any idea why ?