Solution : https://service.sap.com/sap/support/notes/336480 (SAP Service marketplace login required)
Key words :
menu function 'edit -> change field contents', prerequisites solution call transaction se11, additional key words ob07, field tcurv-xbwrl, controlling xpras rtxxbwrl, exchange rate types, exchange rate type, tcurv-xbwrl = 'y', field xbwrl, click 'change'
Related Notes :
| 538416 | TCURR: Rates with reference currency as "To" currency |
| 178128 | TCURV-XBWRL field as of Release 4.5B |