public void SetGridOptions( 
   Map map,
   GridOptions gridOptions
)

{
    //assume
    //var map = MapView.Active.Map;

    QueuedTask.Run(() =>
    {
        //If grid options have not been set for the map, then default grid options are added
        //for the map and returned otherwise the existing gridoptions are returned.
        //NOTE: Grid options are by value meaning a copy is returned. Any changes made to the
        //grid options need to be -set- back on the map using SetGridOptions for the changes to persist.
        var gridOptions = GridOptionsEnvironment.Instance.GetGridOptions(map);
        //change some properties
        gridOptions.RotateWithMap = !gridOptions.RotateWithMap;
        gridOptions.GridLineColor = ColorFactory.Instance.RedRGB;
        gridOptions.GridLineColor = ColorFactory.Instance.BlueRGB;
        //To apply changes, the gridoptions must be set back on the map
        GridOptionsEnvironment.Instance.SetGridOptions(map, gridOptions);
    });
}

{
    //assume
    //var map = MapView.Active.Map;
    var center_pt = MapView.Active.Extent.Center;
    var width = MapView.Active.Extent.Width;
    var height = MapView.Active.Extent.Height;
    var qtr_width = width * 0.25;
    var qtr_ht = height * 0.25;

    QueuedTask.Run(() =>
    {
        //If grid options have not been set for the map, then default grid options are added
        //for the map and returned otherwise the existing gridoptions are returned.
        //NOTE: Grid options are by value meaning a copy is returned. Any changes made to the
        //grid options need to be -set- back on the map using SetGridOptions for the changes to persist.
        var gridOptions = GridOptionsEnvironment.Instance.GetGridOptions(map);

        //Set the grid origin
        var x1 = center_pt.X + qtr_width;
        var y1 = center_pt.Y + qtr_ht;
        gridOptions.SetGridOrigin(new Coordinate2D(x1, y1));
        //or use Coordinate3D
        gridOptions.SetGridOrigin(new Coordinate3D(x1, y1, 0));

        //To apply changes, the gridoptions must be set back on the map
        GridOptionsEnvironment.Instance.SetGridOptions(map, gridOptions);
    });
}

{
    QueuedTask.Run(() =>
    {
        if (GridOptionsEnvironment.Instance.HasGridOptions(map))
        {
            //set back to defaults - will overwrite existing
            GridOptionsEnvironment.Instance.SetGridOptions(map, 
                GridOptionsEnvironment.Instance.DefaultGridOptions);
        }
    });
}