'Replace the Nth occurence of OldValue with NewValue
Sub ReplaceNth(Target As String, N As Int, OldValue As String, NewValue As String) As String
Dim I As Int, Posn As Int, Res As String
Posn=0
For I=1 To N
Posn=Target.IndexOf2(OldValue,Posn)
If Posn=-1 Then Return Target
If I=N Then
Res=Target.SubString2(0,Posn) & NewValue & Target.SubString(Posn+OldValue.Length)
Else
Posn=Posn+OldValue.length
End If
Next
Return Res
End Sub