If you have a file with classes that you would like to emulate, you can place that file in the "Standards" folder within the Vectorworks program folder. Then in your new file create a new class using the "create class from standard" option. You can pick more than one or all of the classes that are in the "standards" file.
After you have brought in the classes you want, you can delete old classes and simultaneously reassign objects in the deleted class to another class. The option to reassign the objects to another class only appears after you click on the delete button (scary, I know).
Adding new VW layers can be done similarly to classes, but deleting VW layers does not perform like deleting classes.