In the simplest case, just add additional labels to your nodes. To do that, right-click a node to open its context menu and choose "Add Label".
A more sophisticated approach would be adding custom properties (see "Edit" -> "Manage Custom Properties"), then preparing a node by adding an additional label for each custom property, then creating a user-defined palette section (see "Edit" -> "Manage Palette") and adding the prepared node as a new node template to said palette section, and finally creating and running a properties mapper configuration (see "Edit" -> "Properties Mapper") that sets the text for the new labels to the values of your custom properties.
Please see the yEd Manual for more information on custom properties, the palette, and the properties mapper.