Customization in salesEditLine form in Ax 2009

Hi friends,

I have added a custom integer field on the SalesParmUpdate table and added that field also on the SalesEditLines form. When the user posts a packing slip on a SO, the system shows the previous values of the SalesParmUpdate table in the SalesEditLines form. I want the system to reset the value of the custom field only (standard Ax SalesParmUpdate fields should retain their value).

Kindly help.

Regards, kiran