Size validation on classificatin attributes and to display all the error in a new pop up.

Hi, We have a requirement where we need to validate the size of classification attribute (may vary on each attribute) in the product cockpit as well as through excel upload. I have extended the classification attribute renderer and I was able to display custom error using the notificationService. But I want to show all the validation errors in the form of a new pop-up and not as notification widget. Is this something can be done through custom widget/action? If yes, how can we invoke the widget from renderer? Could you pls guide?