通过使用以下功能编辑文档的XML，我设法读写了内容类型属性。在Mac和PC上均可使用。

Function getContentTypeProperty(strElementName As String, docDocument As Word.Document) As String

    Dim xmlNode As CustomXMLNode
    Dim xmlPart As CustomXMLPart

    Set xmlPart = docDocument.CustomXMLParts.SelectByNamespace("http://schemas.microsoft.com/office/2006/metadata/properties").Item(1)

    Set xmlNode = xmlPart.SelectSingleNode("/ns0:properties/documentManagement/ns3:" & strElementName)

    If xmlNode Is Nothing Then
        getContentTypeProperty = ""
    Else
        getContentTypeProperty = xmlNode.Text
    End If

End Function

Function setContentTypeProperty(strElementName As String, docDocument As Word.Document, strValue As String) As Boolean

    Dim xmlNode As CustomXMLNode
    Dim xmlPart As CustomXMLPart

    Set xmlPart = docDocument.CustomXMLParts.SelectByNamespace("http://schemas.microsoft.com/office/2006/metadata/properties").Item(1)

    Set xmlNode = xmlPart.SelectSingleNode("/ns0:properties/documentManagement/ns3:" & strElementName)

    If xmlNode Is Nothing Then
        setContentTypeProperty = False
    Else
        If getAttributeValueByName(xmlNode.Attributes, "nil") = "true" Then setAttributeValueByName xmlNode.Attributes, "nil", "false"
        xmlNode.Text = strValue
        setContentTypeProperty = True
    End If

End Function

Function getAttributeValueByName(xmlAttributes As CustomXMLNodes, strAttributeName As String) As String

    Dim xmlAttribute As CustomXMLNode
    Dim strValue As String

    For Each xmlAttribute In xmlAttributes  
        If xmlAttribute.BaseName = strAttributeName Then strValue = xmlAttribute.NodeValue
    Next

    getAttributeValueByName = strValue

End Function