Hello,

loading a cfg file is not possible at any time, only before connecting to the API, so not relevant on how I wanted to use it.

// Define a Preferences File.
            // Preferences file is defined on the IZOSAPIConnection interface (prior to connecting to the API)
            // If no PreferencesFile is defined it will use the default OpticStudio.CFG file however changes will not persist between sessions. 
            // If a PreferencesFile is defined, then any changes will save automatically. 
            Console.WriteLine("===PreferencesFile===");
            string cfgFile = @"C:\Users\Documents\Zemax\Configs\OpticStudio.CFG";
            if (System.IO.File.Exists(cfgFile))
            {
                TheConnection.PreferencesFile = cfgFile;
                Console.WriteLine("PreferencesFile: " + TheConnection.PreferencesFile);
            }
            else
            {
                Console.WriteLine("Default OpticStudio.CFG prefernces used");
            }

So, as it is possible to work on a copy of the system (without any GUI update), I have modified my script to run as a MonteCarlo, and to save the best and worst runs.

Not exactly what I wanted to do, but at least it runs faster.

    (TheConnection,TheApplication,TheSystem) = Connect()

    surfaces = [1,2,3,4,5,6,8,9,10,11,12,13,14,15,16,17]

    nb_run = 20
    Runs = []
    spots= []
    for j in range(nb_run):

        print("Iteration #:"+ str(j))

        # To work on a copy of the initial system
        new_system = TheSystem.CopySystem()

        for i in surfaces:
            prepareSurface(new_system,i)
            # AddA(TheSystem,i,632.8,5)
            AddBC(new_system,i,632.8,0.5,0.1,10,randomize=True)

        # Use compensators defined as variables
        Optimize(new_system)

        # Retrieve the Geometric Spot size for each configurations
        Spot = GetSpot(new_system)

        # Add the system and its result in the list
        Runs.append((new_system, Spot))

    # Sort the list on the max geo spot
    Runs.sort(key= lambda a:a[1].max())

    # Get the name and path of the system to save in the same
    # directory
    name = os.path.splitext(TheSystem.SystemFile)

    # Save the worst run (last list index)
    Runs[nb_run-1][0].SaveAs(name[0]+"_RSI_worst.zmx")

    # Save the best run (first list index)
    Runs[0][0].SaveAs(name[0]+"_RSI_best.zmx")

    TheApplication.CloseApplication()