Solution : https://service.sap.com/sap/support/notes/789200 (SAP Service marketplace login required)
Key words :
grant_nbr type gm_grant_nbr cmmt_item_long type fm_fipex func_area_long type fkber activate, grant_nbr type bapiupdate cmmt_item_long type bapiupdate func_area_long type bapiupdate activate, copy ddic structure bbp_bapimepoitem, copy ddic structure bbp_bapimepoitemx, purchase order item data, purchase order item, bapi structure bbp_mepoitem, assign package bbp_pu, change short text, attached correction instructions
Related Notes :
| 954531 | BAPI_PO_CHANGE: Field values are not transferred |