一例

Sub test()
    Dim dic As Object
    Dim v
    Dim k As Long
    Dim s As String
    
    Set dic = CreateObject("scripting.dictionary")
    v = Cells(1).CurrentRegion.Value

    For k = 1 To UBound(v)
        s = v(k, 2)
        Select Case Right(s, 2)
            Case "AA", "NN"
                s = Left(s, Len(s) - 2)
                dic(dic.Count) = Array(v(k, 1), s & "AA")
                dic(dic.Count) = Array(v(k, 1), s & "NN")
            Case Else
                dic(dic.Count) = Array(v(k, 1), v(k, 2))
        End Select
    Next
    Cells(1).Resize(dic.Count, 2).Value = Application.Index(dic.items, 0, 0)

End Sub

このほうがわかりやすかったかも。

Sub test2()
    Dim k As Long
    Dim s As String
    
    For k = Cells(Rows.Count, "B").End(xlUp).Row To 1 Step -1
        s = Cells(k, "B").Value
        Select Case Right(s, 2)
            Case "AA", "NN"
                Rows(k).Copy
                Rows(k).Insert
                s = Left(s, Len(s) - 2)
                Cells(k, "B").Resize(2).Value = _
                    Application.Transpose(Array(s & "AA", s & "NN"))
        End Select
    Next
    Application.CutCopyMode = False

End Sub