There's absolutely no difference between Zurich and Geneva, with regard to reinstall procedure.
First, you don't have to go to the Buy procedure in any case. If you need to reinstall, the easiest way is, as explained on the manual, and on the sticky thread about reinstalling on this forum, is to use the "Register Serial" to insert the serial in the registry.
However, if you haven't reinstalled Windows (or haven't created a new user account and logging with this one instead), you shouldn't have go into Trial mode to begin with, because by Uninstalling, your serial number is left in the registry and is not removed.
So, what's happened to you, simply shouldn't happen, unless you did something else, like running a registry cleaner after uninstalling Geneva, that perhaps removed your serial from the registry. The "Register Serial" option does only that, it simply re-insert your serial in the registry.