Solution : https://service.sap.com/sap/support/notes/548173 (SAP Service marketplace login required)
Key words :
choose 'goto -> append structure, display user-defined fields, user-defined fields, display structure rfvicn01_alv, program automatically displays, alv field catalog, data element yyid, general contract reporting, select 'data type', user fields
Related Notes :
| 447851 | User fields for the RE general contract |