Hi
check this note [1422974 - Cannot update a form when having UDF with unique key |https://websmp230.sap-ag.de/sap(bD1lcyZjPTAwMQ==)/bc/bsp/sno/ui_entry/entry.htm?param=69765F6D6F64653D3030312669765F7361706E6F7465735F6E756D6265723D3134323239373426]
and this note [1420925 - 'Code already exists' error when update items/BP via excel |https://websmp230.sap-ag.de/sap(bD1lcyZjPTAwMQ==)/bc/bsp/sno/ui_entry/entry.htm?param=69765F6D6F64653D3030312669765F7361706E6F7465735F6E756D6265723D3134323039323526] too.
All the best.