Spire.Presentation 8.9.4 ではスライドの自動切り替え時間の設定がサポートされています

Presentation ppt = new Presentation();
ppt.LoadFromFile("input.pptx");
ppt.Slides[0].SlideShowTransition.AdvanceAfterTime = 1000;
ppt.Slides[1].SlideShowTransition.SelectedAdvanceAfterTime = false;
ppt.SaveToFile("output.pptx", FileFormat.Pptx2013);
ppt.Dispose();

Previous options:
FromCorner1
FromCorner2
FromCorner3
FromCorner4
New options:
FromTopLeftCorner
FromBottomLeftCorner
FromTopRightCorner
FromBottomRightCorner

Presentation ppt = new Presentation();
ppt.LoadFromFile("input.pptx");
StringBuilder stringBuilder = new StringBuilder();
IAutoShape shape = (ppt.Slides[0].Shapes[0] as GroupShape).Shapes[2] as IAutoShape;
GradientStopCollection stops = shape.Fill.Gradient.GradientStops;
for (int i = 0; i < stops.Count; i++)
{
    float transparency = stops[i].Color.Transparency;
    float brightness = stops[i].Color.Brightness;
    stringBuilder.AppendLine("stops" + i + "transparency: " + transparency + " brightness: " + brightness);
}
File.WriteAllText("output.txt", stringBuilder.ToString());

stops[0].Color.Transparency = 0.5f;
stops[0].Color.Brightness = -0.32f;
ppt.SaveToFile("output.pptx", FileFormat.Auto);
ppt.Dispose();