Lou,
although I haven't tried with 8.5.1 yet, I don't remember having any problems with installing a x.y.1 version on top of x.y. It usually installed a new image directory within the existing installation path.
Exporting a config map is easy: version it (yes, that's necessary) and click on the version you want to export. VAST will prompt you for a library name and if you choose a new one it will ask whether you want a 1gb or 16gb addressable one. You want the 16gb variant.
There are some options hidden and spread all over the place to also move required maps when exporting/importing maps, so you can move complete project structures. You can either export from your old library into a .dat file and export from it into the new one, or you can import your existing code from the backup into your new library, either by working from an old image or a new one. So there's a lit of options for you ;-)
Joachim