Patrick, this might not work for EDI orders. In the EDI orders customer info record is used to map the IDoc values. I believe this happens before the order transaction even starts, so it's possible that this user exit won't be triggered. I'm not 100% sure though but if EDI is used it'd definitely be a concern.
As far as the original question goes - the answer really depends on the data volume and update frequency. LSMW would work for once in a blue moon but if it needs to be done frequently and/or by business users then you'd need a program.