While this is not natively possible in the Response section, you can already do this using a success handler > show notification in the General section – not as clean, but works
Could you share an example? What condition would you want to trigger this error?
I am testing this out with a dummy query, so we can share the feedback internally. I have a blank SQL query that doesn't return anything but is technically successful. To throw a custom error message instead of triggering a success handler/success notification, I make my error condition to trigger a custom error message if the query property is empty: