About customizing retrieve mapping:
You can create custom retrieve map function classes. These classes can be used to manipulate, alter, or set custom values for properties that have been mapped in the retrieve mappings.
We recommend creating a custom retrieve function to customize retrieve, rather than
creating a custom property processor.
Location of sample project and readme:
[Drive]:\Program Files (x86)\SmartConstruction\2019\Customization\Samples\SPC_CustomServerHandlers\SPC_CustomRetrieveMapFunction