About customizing filter handlers:
You can create custom filter handlers. The sample project demonstrates how to load a custom filter handler. The assembly name of the filter handlers and the fully qualified class are set as properties on a drawing filter category.
Location of sample project and readme:
[Drive]:\Program Files (x86)\SmartConstruction\2018\Customization\Samples\SPC_CustomServerHandlers\Custom.SPC.Server.FilterHandlers