<button type="submit" class="btn btn-default add_cart_first" name="ms2_action" value="cart/add">
[[%ms2_frontend_add_to_cart]]
</button>
<a class="hide add_cart_second" type="submit" href="[[~idКорзины]]" >
Оформить заказ
</a><script>
$(document).on('click', '.add_cart_first', function(e) {
$(this).hide();
$(this).next('.add_cart_second').show();
});
</script>