A simple macro should do the trick
Code:
Sub Macro1()
Dim oFld As Field
For Each oFld In ActiveDocument.Fields
If oFld.Type = wdFieldSequence Then
If InStr(1, oFld.Code, "Appendix") > 0 Then
oFld.Result.InsertAfter ")"
oFld.Result.InsertBefore "("
End If
End If
Next oFld
Set oFld = Nothing
End Sub
Installing Macros