...

@AutonomousModeAnnotation(parameterNames = {"however", "many", "arguments"})
public class Something extends CommandBase {
    //this constructor is used when the auto is built due to the num
    public Something(int arg1, String arg2, double arg3) {

    }

    ...
}

AutonomousModesReader reader = new AutonomousModesReader(new DataFileAutonomousModeDataSource("/amode238.txt"));
Command autoCommand = reader.getAutonomousMode("whateverItsCalled");
autoCommand.schedule();

...

public class Robot extends TimedRobot {
  private Command m_autonomousCommand;

  private AutonomousModesReader m_autonomousModesReader;
  private List<String> autoNames;
  private SendableChooser<String> autoChooser;
  private String lastSelectedAuto;

  @Override
  public void robotInit() {
    m_autonomousModesReader = new AutonomousModesReader(new DataFileAutonomousModeDataSource("/amode238.txt"));
    autoNames = m_autonomousModesReader.GetAutoNames();
    autoChooser = new SendableChooser<String>();
    autoChooser.setDefaultOption("Default Auto", autoNames.get(0));
    for (String name : autoNames) {
      autoChooser.addOption(name, name);
    }
    SmartDashboard.putData("Auto choices", autoChooser);
    lastSelectedAuto = autoChooser.getSelected();
    m_autonomousCommand = m_autonomousModesReader.getAutonomousMode(lastSelectedAuto);

    
  }

  @Override
  public void robotPeriodic() {
    CommandScheduler.getInstance().run();
    
    if (lastSelectedAuto != autoChooser.getSelected()) {
      m_autonomousCommand = m_autonomousModesReader.getAutonomousMode(autoChooser.getSelected());
    }

    lastSelectedAuto = autoChooser.getSelected();

  }

  ...

  @Override
  public void autonomousInit() {

    if (m_autonomousCommand != null) {
      m_autonomousCommand.schedule();
    }
  }

  ...
}