Private Declare Function FindWindow Lib "User32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function SendMessage Lib "User32" Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Private Const SC_CLOSE = &HF060&
Private Const WM_SYSCOMMAND = &H112

Private Sub Timer1_Timer()
    Dim Num As Long
    Num = FindWindow(vbNullString, "Editor del Registro") 'Esto nos va a dar el hWnd de la ventana cuyo titulo sea Editor del Registro (regedit.exe)
    
    If Num > 0 Then 'si se encontro la ventana
        Call SendMessage(Num, WM_SYSCOMMAND, SC_CLOSE, ByVal 0&) 'mandamos un mensaje para que se cierre
    End If
End Sub