I tried that, but it's complicated. Because I don't want to change an otherwise perfectly running system, I tried to install the earlier version to C:\Mach3-062\ and leave the 066 at C:\Mach3\ . But then, I couldn't get the ESS to connect at all. I got the window where to put the IP address, and then next an errormessage. But fortunately, the 066 version was still launchable. Perhaps, it will work if I uninstall 066 first, but I really don't want to do that. And I don't know which files to change manually to switch back from 066 to 062.
One option would be to move the 066 to another folder and install 062 at the original path. Perhaps I try that.