Solution : https://service.sap.com/sap/support/notes/607888 (SAP Service marketplace login required)
Key words :
'itab external identification' line type, optional import parameter 'i_external_id', standard table key definition, standard key key category, add export parameter 'e_tab_external_id', assign field 'external id', type 'bank_tab_recmn_external_id' underneath 'e_max_external_id', export parameter 'e_tab_external_id', field 'external id', table type 'bank_tab_recmn_external_id'
Related Notes :
| 578319 | Addition of parameters to function module |
| 565029 | Create or change structure in ABAP dictionary |
| 564726 | Creating table type in ABAP dictionary |
| 305789 | Creating messages |