Maybe no.
AIUI, if you plug a Librem 5 into a computer then the Librem 5 will identify as a USB serial port.
I have no idea whether it is possible to alter or extend that behavior. Ideally, it would also identify as one (eMMC disk) or two (eMMC & µSD) mass storage devices, providing that that can be done safely (maybe only possible with the µSD card). Failing that, it could expose MTP functionality, or similar.
(If and when tethering exists, that would be different again.)
So the next best option, for speed, is to take the µSD card out of the Librem 5, put it in your computer (has built-in SD card reader or use USB dongle SD card reader) and pre-load the content.