Solution : https://service.sap.com/sap/support/notes/953954 (SAP Service marketplace login required)
Key words : 
relevant correction instructions, almbapi downgrade kit, reference object, maintenance order, service order, order header, terms co_ih_fill_caufvd_from_iloa, caufvd-tplnr, caufvd-equnr, caufvd-sermat
Related Notes : 
       
| 904504 | Technical reference object cannot be changed with BAPI | 
| 774484 | BAPI_ALM_ORDER_MAINTAIN: Error message IM275 | 
| 708508 | Downgrade BAPI_ALM_ORDER_MAINTAIN -> errors |