If your input file is Excel, then a field containing "12345T" should be recognised as character without a problem. So I assume your input file is CSV. I'd suggest opening it as a report and not a database, then using the floating trap on the field sepaator (",", "|") to get the data into the table. You can define your field types yourself this way.
The issue of confidential data is a constant problem - I've asked Datawatch to provide a tool to scramble data while preserving whitespace & punctuation so that we could look at these problems. In this case, can you not edit the data so that it's just got one line of data for "Mickey Mouse"'s medical record?