Using the example you have provided, you could replace
If counter <> fieldCount Then
outputStream.Write(mytable(counter).ToString() & ",")
Else
outputStream.WriteLine(mytable(counter).ToString())
End If
With:
If counter <> fieldCount Then
outputStream.Write(mytable(counter).ToString() & ",")
Else
outputStream.WriteLine(mytable(counter).ToString() & "What ever you want to write")
End If