That's the standard SugarCube "Saves" dialog in that image.
Actually it's not, each slot has being given an extra Save option so that the end-user can "save over" the current data without needing to use that slot's Delete option first.
As I understand things the layout/contents of the standard Save Dialog is (re)generated each time that dialog is shown. So to modify it's functionally "on the fly" there would need to be some sort of notification event between the time that dialog's content has been generated and the time that dialog is show to the end-user, and I personally don't know of such an event.
This would mean you would need to construct your own custom Save dialog, which I believe is possible using the Dialog API combined with information like that found in the Save Settings section of the Config API and the functionallity of the Save API.