Not sure I'm following completely.
You have a single name column in your source table, and you have a 'shortname' column as well as a 'legalname' column in your destination?
Are you wanting to determine whether the name goes into 'shortname' or 'legalname' based on some criteria?
I think you can accomplish what you're after with a Derived Column transform, but I'll need a little more clarification on your intent first.