Welcome @RyderFine to the Instructure Community!
What I would do is make a copy of the page once you add that "coming soon" message to it. The process is explained in a page in the Canvas Guides: How do I duplicate a page in a course? The copied page is unpublished, and you can edit that without student users seeing it. When you are ready, you can unpublish the "coming soon" page and publish the developed copy of the page. If you link those pages from a module, you could even keep them both there. I would also make the page names different enough so it's obvious to you which one you're looking it at any given time.
