Unable to update user start date

We have a number of manager level users that have start dates after their subordinates, and so are unable to be assigned as managers (confirmed with Oracle that this is standard functionality).

We don't have access to the HCM module, so have been attempting to amend via HCM Data Loader, but have been unsuccessful.

We've used several variations of the code below (as per Doc ID 2154162.1), but each time it ends with the error "The WorkTermsSDO attribute value is required. You must enter a value."

To get around this we've tried uploading the full data set (Employee, Person Name, Address, Email, etc), but it either didn't work, or produced a duplicate record.