The Output Data Table activity only supports comma as delimiter. If you want to use a custom delimiter you need to generate the CSV text yourself. You could e.g. use CSVHelper to write the CSV file. Use the following code in an Invoke Code activity:
Dim sw As StreamWriter = File.CreateText(in_FileName)
Dim csv As CsvWriter = New CsvWriter(sw)
csv.Configuration.Delimiter = ";"
csv.Configuration.Encoding = New System.Text.UTF8Encoding(False)
' Write headers
For Each col As DataColumn In in_DT.Columns
csv.WriteField(col.ColumnName)
Next col
csv.NextRecord
' Write rows
For Each row As DataRow In in_DT.Rows
For i As Integer = 0 To row.ItemArray.Count-1
csv.WriteField(row(i))
Next
csv.NextRecord
Next row
sw.Close
' Clean up
sw.Dispose
csv.Dispose
The line csv.Configuration.Encoding = New System.Text.UTF8Encoding(False)
is actually not needed since CSVHelper seems to write without BOM by default.