When you use hierarchy in design, you add subcircuits into your current design. Schematics,Data Files or EM documents can all be subcircuits of a circuit design and System Diagrams can use other System Diagrams as subcircuits. Ctrl + K is the short cut to add a subcircuit to your current design. When you add the subcircuit ,by default the symbol will be the generic N-port subcircuit, shown below for a two port.
Each one of these documents has a property to assign the default symbol. Select the document in the project tree, right click and select Options. Find the Symbols tab and select the default symbol. The next time you place a subcircuit it will use this symbol by default. The same subcircuit with "email@example.com" as the default symbol will display as shown the next time it is added.
Note: Changing the default symbol does not automatically change the symbol of any subcircuits already in use. For those items, you can can use the element properties to change the symbol or re-add the subcircuit to your design after changing the default symbol.