I can get it to work for text boxes, but not for Org Charts.
Here is the MS Excel VBA Help article and example that I have tried that
illustrates the problem:
TextShape Property
See AlsoApplies ToExampleSpecificsReturns a Shape object representing the
shape of the text box associated with a diagram node.
expression.TextShape
expression Required. An expression that returns one of the objects in the
Applies To list.
Example
The following example adds child nodes to a parent node, and displays text
in the parent node indicating the number of child nodes created.
Sub CountChildNodes()
Dim nodRoot As DiagramNode
Dim shDiagram As Shape
Dim intCount As Integer
Dim shText As Shape
Set shDiagram = ActiveSheet.Shapes.AddDiagram _
(Type:=msoDiagramRadial, Left:=10, Top:=15, _
Width:=400, Height:=475)
Set nodRoot = shDiagram.DiagramNode.Children.AddNode
' Add 3 child nodes to the root node.
For intCount = 1 To 3
nodRoot.Children.AddNode
Next
' Change text in node.
For intCount = 1 To 4
Set shText = shDiagram.DiagramNode.Children.Item(1).TextShape
shText.TextFrame.Characters.Text = Str(intcount)
Next intCount
End Sub