I looked at the documentation, and the way to make an analogous function to 'insertAfter' except for XML is as follows:

Sub InsertXMLAfter(ByRef newDoc As Document, ByRef strXML As String)
  Dim rng As Range
  Set rng = newDoc.Content
  rng.Collapse Direction:=wdCollapseEnd
  rng.InsertXML strXML
End Sub