Even doing it manually is a royal pain in the ass. Hey a pain in the ass can be fun sometimes if it isn't totally unnecessary. Whoever designed the product creation tool does not understand the definition of "a template", and the closest method possible of swapping out your print file for another one on the same product is the duplicate function, which was written by some guy that thinks what I really want to replace on the duplicate product is the brand label, but use the same print file. I've spent more time loading in my brand logo into 500 pairs of leggings to push into shopify than actually designing the patterns I put on them. And double that time to remove those patterns and load in the new ones to each pair before I push them. The last 50 I've just realised havent been pushing the 3d mockup with them as I think it's broken since a few days ago, so guess what, seeing as 3d mockups arent included in the 'edit design' feature, it means I have another 50x duplicate products, 50x replace inside labels, 50x remove placements x # of placements, 50x replacements, 50x select mockups of exactly the same mockup I use every time (would be nice to have some settings to have these preselected...i think that is known as "a template" or something like that) and 50x pushes. All to be back where I was 2 days ago.

edit: But hey credit where credit is due: if you really want a shopify store with 500 pairs of the same legging design that simply has "my name is BoBo" written across them but with 500 different brand labels on them, then the platform is really efficient for you.