The method is really fast once you have set the correct rectangle selection tool options: In each image, you just need to click and move the selection to the correct location. But when you create a new selection, it has the dimensions expected. I can confirm that this solution works, although it is very worrying that the selection in the first place does not change when you enter new dimensions in the "Size" field.
The following solution has been posted by here. The method in Kerr's answer is working, but I'd like to share an alternative method I have been shown in the meantime. However, for rectangular selections/paths, there is no approximation so the copy is accurate. i have used many tools for image resizing, maintain resolution.
#Graphic converter mac lasso tool forced aspect ratio free
Note: technically, this solution could work for any arbitrary shape, but in the general case, the path is an approximation of the selection, and the selection is an approximation of the path, so the selection in the target would be a double approximation of the selection in the source. But you can reduce image size without reducing quality, in Photoshop, via free web tools. If you need to repeat on several images, you can reuse the path, so repeat from step #3.