There’s actually a pretty easy way to do this! Find out more here: Edit the template applied to existing content
Here’s a video as well (might be a little outdated): https://www.youtube.com/watch?v=LRUQvmsWPFQ
As far as the URL, it should stay the same as you are just changing content. However, I’m not superrrrr experienced with Hubspot landing pages so don’t quote me on that 