I think following approach should address your use case.
1. Have separate variable defined for ST1.COLUMN09, ST2.COLUMN01, ST3.COLUMN02
2. Create a package add refresh steps for these variables
3. Create the interface and conditionally assign value based upon your criteria. Eg. <@if (business unit = 'A')@><@=#varST1@>
4. Add interface tot eh package after refresh steps.
5. Generate scenario and execute it.