What happens when I change my landing page's Publish URL?

Using our new UI? You might want to check this help article instead.

Changing your landing page's url is super-easy!

Once you have clicked on the landing page you wish to work on, click on the Publishing step, then select one of the available domains from the drop-down menu in the first field and type in your desired path in the second.

When you change your landing page's url, the landing itself remains intact and active throughout the process. The only thing that changes is the url, which is updated to whatever you changed it to.
So feel free to change your landing page's publish url at any time, as this will not affect your landing page in the slightest!