Programmatically edit Step.Datasource

I'm creating a LabVIEW tool to update several step properties after some needed changes.

One of the changes was a step type went from a numeric limit test to a boolean pass/fail. 

Since I couldn't have all of the customers sequences (several hundred) loaded when I made the changes, I need the tool to change the Data Source for this step type from "Step.Result.Numeric" to "Step.Result.PassFail". Problem is I can't seem to find the right combination of properties/methods to make it happen.

I don't see a 'Step.DataSource' property like there is for the 'StatusExpression' and 'Precondition'. I've tried taking the "AsPropertyObject" ref from the Step ref, then using 'SetValString' method to set "Setp.DataSource" to "Step.Result.PassFail", but this returns a -17306 error that returns "Error accessing item 'Step.DataSource'."

Thanks

Ed