Answer:

Web Creator makes these operations impossible. Web Creator projects are saved in a proprietary format and converted to HTML when preparing for web. Web Creator cannot read HTML, PHP, ASP, etc. files, it only reads files that it created itself. Web Creator can't even load it's own HTML output, so it's very important to keep your project source safe. Without it, you will not be able to modify your Web site.

Furthermore, Web Creator projects cannot be opened or modifed with those other HTML editing software. Web Creator uses javascript almost exclusively to create it's output, making the actual HTML output almost void. A client with strong javascript knowledge could be able to open and modify the web output, but those modifications could not be loaded back into Web Creator for further modifications.