I have several libraries (not he internal library, I don't use that) on my hard disk, and can call objects (and terrains, or clipfiles) from there. As long as you don't change the folder structure or location of objects and textures, it will be ok. Even if you change the location of the saved TGD. On my other machine I have exactly the same folder structure, so if transferring a tgd, it will call the objects from the 'same' locations.