When changing sales document in transaction MASS with object BUS2032, it is not possible to change field "Ship-to Party's Purchase Order Number"
(VBKD-BSTKD_E) since the field is not defined in field list of the object.
Here, I would like to share a solution to solve this problem.
1. Call transaction MASSOBJ.
2. Highlight object type BUS2032.
3. Double click on "Field list(optional)" in "Dialog Structure".
4. nput "Work Area" from BUS2032 to BUS2032 then press "Continue".
5. Press "New Entries" button.
6. Input "ObjectType" BUS2032, "Table Name" MASSSDPOSVBKD and "Field Name" BSTKD_E.
After these steps, the field should be listed and can be used in MASS change.
Hope this information is helpful