When importing data to master record tables like item, customer, vendor, etc. it would be really helpful to have a setting (boolean) on the table section of the config package where you could check that you only want to modify and NOT create records. I have had many instances where the imported data records contains new records that you may not want to create and the Modify Only setting would resolve this. For records not existing they would be sent to the errors just like when loading sub tables where the master record does not exist (i.e. bom line where the item doesn't exist). An alternative might be to place the boolean at the field level (i.e. for items on the No. field where the code would then check to see if the No. exists before creating a new record).
This would be a really simple addition as it would just be an additional Boolean which would drive a validation event to make sure the record exists before creating a new record.