wyUpdate rolls-back updates only when the user cancels an update mid installation, or when an error occurs in the update process.
But I know what you're talking about, you want to roll-back to versions after an update has been successfully installed. Unfortunately we don't support that. And it's not on our planned features.
The reason is that we can't make assumptions about your product. That is, does it support backwards compatible filetypes, settings, etc? Plus there are other problems. File size is one - I don't know about your product but most of our customers have products that run in the several gigabyte range. So if we kept every previous version just hanging around then a few simple patches could quickly fill up a user's hard drive. (Patches are one-way, we would have to back up full files if we wanted to keep old versions).
I would recommend letting the user re-download an old installer if they want to use the old version.