可以执行以下操作:

var $mainElem = $('.row'),/* adjust selector to suit page*/
    $parent = $mainElem.parent(),
    /* remove children after 4th from existing row */
    $items = $mainElem.children(':gt(3)').detach();

if ($items.length) {
    /* create new row for every 4 items removed above */
    for (var i = 0; i < $items.length; i = i + 4) {
        var $row = $('<div class="row">').append($items.slice(i, i + 4));
        $parent.append('<hr class="divider">').append($row);    
    }
}

演示