Sub test()
     Dim p$, f$
      
     p = "Диск:\Путь к файлам\"
      
     f = Dir$(p & "*.xls*")
     Do While Len(f)
         With Workbooks.Open(p & f, False)
             .BuiltinDocumentProperties("Author") = "Новый автор"
             .Close True
         End With
         f = Dir$
     Loop
End Sub

Sub sdf()
      Dim strFolder$
r:  With Application.FileDialog(msoFileDialogFolderPicker)
          If .Show Then
              strFolder$ = .SelectedItems(1)
          ElseIf MsgBox("Ничего не выбрано. Повторить?", 36, "Ну так как?") = 6 Then
              GoTo r
          Else: Exit Sub
          End If
      End With
      Dim strFile$
      With CreateObject("DSOFile.OleDocumentProperties")
          strFile = Dir$(strFolder & "\*.xls*")
          Do While Len(strFile)
              .Open strFolder & "\" & strFile, , 2
              With .SummaryProperties
                  .Author = "Новый автор"
                  .lastsavedby = "Новый автор"
              End With
              .Save: .Close
              strFile = Dir$
          Loop
      End With
End Sub