I just made the huge mistake of updating from 6.2 to 6.4 on my laptop at a customer site.
Unfortunately for me, the MacOS upgrade wipes the existing 6.2 installation and the 6.4 installation asks to relicense. This is problematic because I am in a remote location and don't have access to my original install information at this site. I am now twiddling my thumbs in front of a customer while I wait for Cadsoft USA to resend my licensing information having wiped the working installation from my machine. Cadsoft has always been great with customer support and I am sure it will be handled promptly, but it is annoying.
You need to either leave the working installtion in place or at very least pull the license info from the old directory. Wiping my working executables and leaving me high and dry is just not a cool thing to do.