Hello @Master_Over_Sun
I'm not fully sure what your exact goal is, but just to clarify, you can customize Kintone’s built-in print layout to some extent using the app.record.print.show event.
However, if you're aiming for more advanced control, such as restructuring the entire layout or adding a header that repeats on every printed page, this isn’t possible with the built-in print view.
In that case, you'd need to create a custom print page using JavaScript to open a new window or tab and generate the layout manually. Here’s a related resource that includes examples of creating a custom print page: Bulk Print Records (list view) each record it’s own PDF