alluded to with his post at the top of this page, if you don't want to get into editing the xml file and just want to move the library to save space on your start up disk and/or put it on an SSD, the easiest method is simply to move your Vectors folder to the disk of your choice, create a symbolic link to it and put that link in the Nebula3 folder (after deleting the original Vectors folder) You could move the Programs folder too, but it really doesn't use that much space, so I didn't bother.
You don't have to use the Terminal to create the link either. Here's a page where a kind chap has written an Automator workflow that installs a 'Create symbolic link' service that you can access by right clicking on the folder you want to link to:
https://tumbleseed.wordpress.com/2010/0 ... k-service/
He mentions that you have to open it in Automator and save it to the Services folder, but I found (on 10.10.5) that double clicking the unzipped workflow generates a dialog asking if you want to install it as a service. If you click 'Install' it simply moves the workflow to home folder/Library/Services.
Now right click on your newly moved Vectors folder and select 'Create symbolic link' You should see what looks like a Mac Alias appear called 'Vectors link' Copy this back to your Nebula3 folder and rename it to just 'Vectors' If you click on it you should see the contents of your Vectors folder on the other disk and so will Nebula. You can delete the 'Vectors link' link left sitting next to your Vectors folder on the other disk.
Bear in mind if you move the Vectors folder again, you will have to recreate the link. It won't follow it like a Mac Alias will.
Incidentally, if you're a Logic Pro X user and you'd like to move that ~15GB GarageBand folder in Application Support off your start up disc, this technique will work for that too.