Solution : https://service.sap.com/sap/support/notes/103559 (SAP Service marketplace login required)
Key words : 
distribution -> sales -> sales documents -> define variable messages', open quotations/outline agreements exist, additional key words mv45af0m, sales order type, prerequisites solution implement, 'variable messages', function 'propose items', screen sequence control, source code corrections, open quotations/contracts
Related Notes : 
       
| 74055 | Variable messages: Version maintenance |