I am not sure if I understand your question. Element Properties & Classifications are, as the name implies, on single Element basis. You can't do further calculations of multiple elements in one element's properties. But you can set additional properties to an element which can be derived from one or more already set properties of that same element. Classifications are one further step for correct data exchange.
For further calculations of multiple elements properties you need to use schedules. You can set a schedule to calculate and display composite skin calculation results. Here a quick sample:
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