Also using Logic Pro version 12. I just want to be sure that I can redirect updates and that Logic Pro will pull from the new location (external drive) so that I can comfortably delete the "Shared" folder on my internal drive.
I did this with all my libraries a few years back.
First I modified the Content Location in the File Preferences to point to the appropriate location for any new downloaded libraries. I NEVER change the Application or Download locations as that's not recommended by NI. This really only affects NEW downloads, so I sometimes change this to point to different locations depending on the vendor or library I'm downloading.
After that I moved the original libraries one by one over to their new home directory, and renamed the old directory to make sure that link was broken, but not deleted yet. That allowed me to use the Locate function in Native Access on the moved library to ensure it was the one now being used by Native Access, Kontakt and Komplete Kontrol. Once I was certain that was working by testing it in my DAW, I deleted the old renamed library.
There are other more automated ways to do this now, but I wanted to be very cautious to make sure everything was working with the move before going on to the next library.
Be aware that the speed of the drive you're moving it to can have a significant impact on how things work after the move. In my original case I was moving from an internal hard drive to a high capacity SSD, so my performance on those libraries improved considerably.
