can't programatically update line item on drupal commerce order
Recently I've updated some other line item fields on commerce_add_to_cart_submit() via this code:

$line_item = commerce_line_item_load($lit_id);
$line_item-&gt;field_product_options[LANGUAGE_NONE][0]['value'] = $size;
commerce_line_item_save($line_item);
entity_get_controller('commerce_line_item')-&gt;resetCache(array($line_item-&gt;line_item_id));


I hope this will help someone.