How to change several images in gimp that are already open

normally i'd just use imagemagick's convert, but I had a bunch of scaed images that i had to crop the content which was all over the place.

So i opened some 30 images on gimp, manually cropped them all. Now I found myself wanting to resize them to 66% of the size and export them all to their original name (they were open from PNG images)

and i realize there is no easy way to do that. or is there?

All searches tell me to use command line or scripts. but nothing that will work on already open images via the UI.