The context menu in RadFilter is a shared control which holds all available options in its items and only the necessary ones are shown when you click on a button according to the data type of the field. That's why any modifications regarding showing and hiding of items in the menu should be done on the client at the point when the menu is showing for a particular field. If you know for which field exactly the menu is about to show you can handle its shown event and modify the visibility of the items according to your needs. If every field requires different options in the menu then this information should also be available on the client (for example you can serialize it from the server).
Currently RadFilter does not provide an easy way of manipulating the items in the context menu, that's why custom client-side approaches are required to achieve the desired effect. For more information you can refer to the client-side APIs for RadFilter and RadContextMenu:
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