A child theme with all of the template files would definitely work.
Anything in your child theme is used before the parent theme, so if you add those templates to your child theme, the stuff in GP will be ignored in favor of your custom files.
This post veered off topic from the main topic but I’d still like to see the category link under each post on the archive page removed. Unless I’m missing something the category link doesn’t serve any purpose being there as it only links to the page you are actually on. Removing the category link will use less real estate to!
Hmmm, hangon, what about posts with multiple categories? This allows the user to click on the other category. Is this worth keeping it though on the archive page? I mean they can always see the other cat on the post page!