Changing your landing page's url is an easy task to perform.
1. Once you have clicked on the landing page you wish to work on, click on the Choose publishing method step on the menu available on the left.
2. 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 page 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.