Todd, this is difficult one but the process you described is the best method in what you want to do, you probably will have an extra step though:
- Create the new page.
- Copy the original URL over to the new page and add a hyphen ( - ) onto the end (as 2 pages can not have the same url at the same time in Marketo).
- Delete the old page.
- Remove the hyphen ( - ) on the new page url
Form a content point of view this will be ok, but since the new design will have new HTML, etc... this may effect your ranking on SEO.
I believe it may be better to setup 301 redirect and keep both pages and two URLs...which is what happens when you do the redirect in Marketo.
The other method Greg describes will work, but it may affect ranking initially. You also lose the original page.
If you're set on having the same URLs, then you'll have to do the swap out where you're quickly changing the URLs one after another. If you do this quickly enough (in less than a day), the process itself probably won't have any impact on SEO—Google and other search engines crawl your site on the order of once per day for the most part, so you'd probably be able to make the swap before it recognizes that the original URL is broken.
If you're not set on having the same URLs, a much easier and less stressful approach is what Josh mentions. You can create all of the other landing pages on a separate URL, then in the Admin section create 301 redirects from the old URLs to the new URLs. In my experience, this is easier to implement because you can track it all with an Excel sheet and make the changes much faster overall.