The selectCallback function is called whenever a user selects a different option through the options dropdown menu, and it’s used to update the variant’s price and Compare At price. Since the image-swapping needs to happen when the user selects a different option, why not place our JS in selectCallback? 😀
What you can do is place the code in the Step 3 inside the selectCallback function, which is usually located in “product.liquid” or “theme.liquid”. In Radiance, it is located at the bottom of “theme.liquid”.