modify xml report header

I wish to modify the XML header by adding an extra line of text. I tried the ModifyReportHeader callback using the expression:

Parameters.ReportHeader += Locals.my_new_text.GetXML(XMLOption_NoOptions, 0, "", Parameters.ReportOptions.Format )

This does not work, just does not show up at all in the header. Does anyone know why or have an example that works (TestStand 12)?