Codepen is a teaching tool, a place to try things out and learn things. It is not “real” web development. It is the difference between using a flight simulator and actually flying a plane.
But yes, if you edit the code for the site and incorporate the site correctly, they should be useful.
I have not done shopify. Am I correct in assuming that by “Shopify website” you mean a standard website that uses shopify? Are you able to edit it at all? That would be my first step, to confirm that I understand how to make any change to it.
Unless someone has some specific knowledge here, I think we’d need to see the site in question. Is there a repo?