If its a drastic change, then I'd suggest to have a copy of the entire website to a sub domain and do all changes there. Then after done point the sub domain to main domain or move all the files and database to root. By this way you can edit your site without any major downtime.

Rony

I am assuming that you have Hosting control of the Web server (Apache hopefully) and your section of the file system that you're website is on. Copy your whole web site's root folder and everything in it to a new folder with an appropriate name. With Apache, In your /etc/httpd/conf.d subdirectory, Copy your web site's config folder to something like work.conf and in it, change the 'ServerName' to something like 'work.yourdomain.com' and then change the folder name to match the folder name you gave to the work site. (don't forget to re-start Apache) Then, log into the work copy of your website as admin and put it into maintenance mode so you are the only one that can see it. When your done, just swap the names on your root folders to put your new work on line.

Also, depending on what method you use to copy your site, you might have to straighten out folder & file permissions to get the copy you made working.

By the way, if you are only working through Concrete5's editing and dashboard proceedures and not doing any hard coding, Your work doesn't become viewable to the public until the current version of the page you are working on is approved. Until then, the last approved version is what is shown to the public. If you are doing a lot of work, it is best to copy your site to a test site just in case.