A customer had a large number of reports all scheduled to unmanaged disk. The issue was that the OS account they were using to write to the disk drive was changing and they did not want to have to reschedule every report.
The following code can be used to update the username and password on the recurring object itself so that it does not have to be rescheduled.
NOTE: This is completely unsupported to do and any issues you run into will not be supported by SAP support. The official supported method of changing anything that has to do with a recurring instance is to reschedule the instance. Make sure you thoroughly test this before using it. You have been warned!
Update OS user account used for scheduling in VB.NET
Good luck with your projects!