I’d give this a try:
Connect your external drive.
Make an NTFS file system junction to your external drive in the “%SYSTEMDRIVE%/ProgramData/Steinberg/Content/Halion/Vst Sound” directory.
Open a command line prompt in admin mode. Enter something like:
mklink /j "C:/ProgramData/Steinberg/Content/Halion/VSTsound/ExternalDriveF" "F:/HALion Content"
Install the libraries to that junction directory using the Steinberg Librarian utility. The files will actually go to the external drive, but the OS sets things up so apps behave as if it’s all on the C drive.
When using the PC without the external drive, my guess is that those sounds might still ‘show’ in the database, but cannot be used. Maybe with some sort of markers (red exclamation points?) showing the file isn’t present. If some project tries to use those sounds, you’ll probably get nag dialogs about it.
If for some reason that junction link goes bad, you can always remove it or fix it without destroying the actual content on your drives (deleting the LINK doesn’t delete the target itself).
I’ve been using hard filesystem links on windows for years without any problem. On some systems I even make little batch file scripts that’ll autorun when a device is plugged in, and build/remove such links as needed. It’s pretty powerful stuff, and to me it’s far simpler than constantly creating and ‘moving/removing’ wads of ‘windows shortcut’ files around with the mouse.
In some cases you might want or need to force Mediabay to rescan everything. From time to time you might need to ‘ignore’ some ‘nag prompts’ if that external drive isn’t plugged in.
If for some reason Cubase gets far to ‘naggy’ to be useable without the external drive plugged in, then you still have some options!
I’d have to dig deeper to see where Cubase keeps the mediabay db, but it should be possible to keep some mirror copies and ‘rename’ the parent directory as needed to swap between your different configurations.
You might even make things simpler by using two different User Logins.
Use one account for when you have all the drives plugged in.
I think Cubase can be configured (if that’s not already the default) to keep a different db for each ‘user login’.
Make a different login account for on the road use. This way you can get a fresh set of user %appdata% directories to host a unique set of conditions for apps to abide by. You’ll still have the ability to ‘copy’ things from one setup to another (commonly used preferences, keycommands, remote scripts/settings, etc)…but then you can fork the two setups off in different directions depending on what each ‘account’ needs.
By this I mean…stuff you install when using the primary (everything is plugged in) login account can be different from the stuff you install while using a different (I’m on the road and have fewer/different things plugged in) User Account.
With a little experimentation you should be able to sort it all out.
Experimenting with a couple of different OS/desktop login accounts might be well worth the effort! After all…when on the road…we tend to carry and plug in different devices and controllers…and keep things to a minimum! So, give it a try. Make a new user account, run some tests, and see what happens.