You are right. The documentation is often wrong. The documentation on CustomXMLParts is deplorable. The documentation is not only often wrong. It is often more complex than in needs to be. In this case, I would have simply used:
Code:
Sub ScratchMacro()
'A basic Word Macro coded by Gregory K. Maxey
Dim oRng As Range
Set oRng = ActiveDocument.Range
oRng.End = ActiveDocument.Range.Paragraphs(1).Range.End - 1
oRng.InsertAfter " This is now the last sentence in paragraph 1"
lbl_Exit:
Exit Sub
End Sub