A MapPoint is based upon the parent Geometry class. The Geometry class is immutable which means that you can not change its shape once it is created. If you need to modify a MapPoint once it has been created, use the MapPointBuilder class instead. The MapPointBuilder.ToGeometry method will provide you with the MapPoint object.
System.Object
ArcGIS.Core.Geometry.Geometry
ArcGIS.Core.Geometry.MapPoint
Target Platforms: Windows 10, Windows 8.1