Yes, you can edit an existing published setup. Please note there are certain fields — grades, residential status, student type — you will not be able to edit once the setup is published. Other than the aforementioned, all requirements, dates, events can be edited even after the application has been published.
Click on the edit button next to the published setup. This will show you a count of students who would be impacted by the changes you would make to the setup. An important note on editing — when you edit an existing setup you are changing the requirements for students who might be in the process of applying or who might have applied already. Any additional requirements might cause confusion and anxiety.
Please note, your application from last year can remain active along with the application for the new school year.