The URL structure for Shopify is set in stone and cannot be altered. The only thing that can be changed is the page/product/collection handle under the SEO settings within each respective page. Shopify is built on Ruby on Rails. Ruby on Rails uses something called routing that uses paths to pull information from the Admin. This method keeps everything clean, speedy, and visually digestible.
If you wish to alter an existing handle, Shopify will create a URL redirect. In which case it would be wise to resubmit your sitemap to have your website crawled again for search engines.
I hope this helps. If you have any other questions, please let me know.
Holly | Social Care @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog