Setting the value of field thats part of packages machine in item fulfillment record

I am trying to set a value of a field which is part of the 'packages' machine which is part of the item fulfillment record. I am doing this in the beforeSubmit event.. It does not seem to commit to the database. Here is the code, Can someone help?

function _BeforeSubmit(type)
{
var i;
var currentRecord = nlapiGetNewRecord();
if (type.toLowerCase() == 'create')
{
//currentRecord.setFieldValue('memo','test'); //this works
for(i=1; i <= currentRecord.getLineItemCount('packagefedex'); i++) 
{
currentRecord.setLineItemValue('packagefedex','deliveryconffedex', i, 5) // this works too
//throw currentRecord.getLineItemValue('packagefedex','deliveryconffedex', i) // this works too, returns 5
}
}
}