Using Addins to Set-up New Hires PR12

Hi,
We receive a file from an onboarding web site as our employees are hired which contains their PR12/direct deposit information.     Each employee may have up to 3 deposit records.

Has anyone done much with the PR12 upload for new hires?   It seems to be working very well for me with a single upload record, but, when I get multiple, it always wants to make the first record the Default Account and I haven't found away to have it auto-assign ACH Distribution Number.

Also, we get a substantial number of rehires.     I'd like to disable or delete any previous PR12 records.    Any best way to do this?

The PR12 seems a little flaky, giving me unpredictable results, so, I'm pretty sure I'm missing something!    Any insight would be appreciated.

Thanks
-Matt