For an existing SQL geography @g, below is code that will extract the points and re-create a polygon with points (vertices) in reverse order:<br>
*(NOTE 1: works for simple polygons, not for multipolygons or polygons with rings/centroids)*<br>
*(NOTE 2: using SRID 4326 (WGS 84) coordinate system)*

    --For existing geography @g
    DECLARE @GeometryText varchar(max), @ReversedPolygon geography
    DECLARE @GeometryType varchar(20) = 'POLYGON', @Count int
    SET @Count = @g.STNumPoints()
	WHILE @Count > 0
	BEGIN
		SET @GeometryText = @GeometryText + CONVERT(varchar(30),CONVERT(decimal(12,8),@g.STPointN(@Count).Long)) + ' ' + CONVERT(varchar(30),CONVERT(decimal(12,8),@g.STPointN(@Count).Lat))
		SET @Count = @Count - 1
		IF @Count > 0 SET @GeometryText = @GeometryText + ','
	END
	SET @GeometryText = @GeometryType +'((' + @GeometryText + '))'
	SET @ReversedPolygon = geography::STGeomFromText(@GeometryText, 4326);