One way I sometimes proceed is to get my image to a state ready to export, then Ctrl-D to duplicate the image. Then I resize as needed, and export to what I want.
If I’m exporting to jpg, I’ll check the box to preview so I can see the filesize, and adjust settings as needed until I’m happy. (I’m usually more worried about filesize when I resize for web, otherwise I’ll just post full-resolution in many cases.)