I don't know how Vesys may be different from Capital on that point, but in Capital, Capital Project, for each project, we have the "OTI" that is the "Object Type Information". in these project section, you can, for each object type that exist in Capital, the availability to define a set of predefine name for the object, or a predefine set of properties for the object. so, in OTI - Harness Diagram, you can add all your properties, and you can define if the property need to be created with any new object (in this case, at each diagram creation). You can force a default value, or provide a list of available value. If you provide a list of value, they will appear as a Drop Down menu in the Diagram properties.
Also, every property you add in this OTI will be available in the properties list when you click on "New" property in the Design or Diagram property interface.