Adding fields to sales packing slip in AX 2012


I need to add some custom fields in sales packing slip. (Account Receivables -> Common -> Sales Orders -> Pick and Pack -> Packing slip) which will open SalesEditLines form. I understand that the data displayed is from SalesParmTable. I need to change the way packing slip journal will be posted. I have already add the custom fields to SalesParmTable and got them displayed in SalesEditLines form. I would like to know in which class the posting process happen so I can modify the posting process? I have already look in SalesFormLetter_PackingSlipJournal but can't seem to find where the tables are inserted.

 In AX 2009, I can change something like SalesFormLetter_PackingSlip.initJournal(), but I can't find such function in AX 2012.


Any help is appreciated. Thanks.