Hi Bruno,
I do not have a personal experience with such a request, but program RFFOM100 (that generates an MT100 file) contains a checkbox "Currency in ISO code" and so does RFFOEDI1 (the most common program for generating payment orders). Have you tried this?
The prerequisite is that the correct ISO code is maintained in config (SPRO: SAP Netweaver - General settings - Currencies - Check currency codes; link is also available from the documentation to the "Currency in ISO code" field in both programs). If it is not - then you will either need to change it (but beware - it may be used in other interfaces or applications) or enhance the payment media program(s).
Good luck!
