The Properties view provides a field in the General tab to edit the default value of a parameter or attribute. However, if the default value is anything but a small and simple value, it's better to edit the default value using the Code view or Code editor. This is especially true if the default value spans multiple lines.
If you select an attribute or parameter, you can edit its default value using the Code view. You can also press the button Edit in code editor that is located immediately to the right of the "Default value" field in the Properties view. Another way is to simply double-click an attribute or a parameter in order to open the Code editor to edit its default value.
The default value of an attribute or parameter is not generated within a user code section in the target code. You therefore cannot load the generated source file into the Code view or Code editor when editing a default value. You also cannot edit the default value inside the generated file and synchronize the changes back into the model.