If I understand correctly, the following will do what you require, at least with your sample document.
If you want the strings added before any existing text between the heading sections then remove the two optional lines.
Sub Macro1()
Dim oPara As Paragraph
Dim oRng As Range
Dim lPara As Long
Dim sHead As String
Const sList As String = "0123456789.)"
For lPara = ActiveDocument.Paragraphs.Count To 1 Step -1
Set oPara = ActiveDocument.Paragraphs(lPara)
If oPara.Style Like "Heading ?" Then
If Not Right(oPara.Style, 1) = sHead Then
sHead = Right(oPara.Style, 1)
If lPara = ActiveDocument.Paragraphs.Count Then 'optional
oPara.Range.InsertParagraphAfter
End If 'optional
Set oRng = oPara.Range.Next.Paragraphs(1).Range
oRng.Text = oPara.Range.Text
oRng.Style = "Normal"
oRng.Collapse 1
oRng.InsertBefore "("
oRng.MoveEndWhile sList
oRng.InsertAfter ")"
End If
End If
Next lPara
lbl_Exit:
Set oPara = Nothing
Set oRng = Nothing
Exit Sub
End Sub