I found out a way to add files to an existing folder with IPFS thanks to this question: IPFS: How to add a file to an existing folder?
but I was wondering if there is a similar solution using Pinata service？
When you update your directory, push the new directory to Pinata via their pinning service like normal. Then, combined with the answer you linked you'd update your new IPNS address to point to the new CID.
This way you can share the single IPNS address, still update the contents, and Pinata will still have your data available to be served.