public RasterMosaicOperatorType MosaicOperatorType {get; set;}

{
    //Note: needs to be called on the QueuedTask
    // Get the image sub-layer from the mosaic layer.
    ImageServiceLayer mosaicImageSublayerToUse = mosaicLayer.GetImageLayer();
    // Get the mosaic rule.
    CIMMosaicRule mosaicRule = mosaicImageSublayerToUse.GetMosaicRule();
    // Set the Mosaic Operator to Mean.
    mosaicRule.MosaicOperatorType = RasterMosaicOperatorType.Mean;
    // Update the mosaic with the changed mosaic rule.
    mosaicImageSublayerToUse.SetMosaicRule(mosaicRule);
}

{
    // Get the mosaic rule of the image service.
    //Note: needs to be called on the QueuedTask
    CIMMosaicRule mosaicingRule = imageServiceLayer.GetMosaicRule();
    // Set the Mosaic Operator to Mean.
    mosaicingRule.MosaicOperatorType = RasterMosaicOperatorType.Mean;
    // Update the image service with the changed mosaic rule.
    imageServiceLayer.SetMosaicRule(mosaicingRule);
}