IS THERE A WAY TO LOAD SINGLE PERFORMANCES FROM A USER OR LIBRARY FILE WITHOUT LOADING THE ENTIRE LIBRARY?

No.

Once you install data to a Library (ROM), you can move (Import) Single Performances from the Library. Because a Performance requires all components that make it work (Waveforms, Samples, Arpeggio, User Curves, Motion Sequences, etc) Montage must assemble all those components and make them available for transfer to your USER Bank. A Performance can be a lot of different components.

So you must first install the File to ROM (Library) then you can have the Montage select the data you want > you Import Library data to your internal USER area, where you can further customize it and create a new Bank. That's how it works. You can then remove the original (temporary) Library, and install you edited version.

If you would like to easily manage your own single Performances, try the computer utility MONTAGE CONNECT. Runs as a VST3/AU plugin or as a standalone application for Windows or Mac. It allows you to capture (via MIDI Bulk Dumps), Save, and Load a single Performance in a .X7B file... and if you are using Cubase you can use the MediaBay > Sound Browser to organize your single Performances.