Exporting a catalog, then importing same catalog with changes to the images

Since I don't have a large format printer, I plan to export images from my main catalog as a catalog to an external drive. I take the external drive to another location for printing. I generally need to make some changes to the images. Now how to I get these images, with the changes, back into the catalog from which they came? I want the images in the main catalog updated, reflecting the changes made while working at the printing location.

Suggests much appreciated.

Cheers,

John