There are two parts: The website, and its corresponding database. The database location isn't your problem here - it's the website itself.
If you One-Click (Advanced) install Wordpress to www.example.com, then later want One-Click (Advanced) Zencart to be www.example.com, you're in for a challenge. You can move a One-Click to be a subdomain, but it'll drop out of the One-Click system, thus leaving you to do your own updates and such.
Through a bunch of hoops, you can trick the system, but it involves a new One-Click to the desired location, then subbing in the old one and its database to that new location.
Naturally, it's best to get it right the first time. But there are ways to change your mind without losing all of your work.