Perhaps one could have the perspective that the modem has the necessary certifications (if indeed it does). The Librem 5 is not itself a radio. However that is the kind of logic that does not sit well with the bureaucrats.
By way of analogy, I can plug a USB dongle into my laptop and the USB dongle will access the cellular network, and has the necessary certifications to do so. My laptop never had certification to use the cellular network. What is the distinction between plugging in an M.2 card and plugging in a USB dongle? and where is the boundary if there is a distinction?
Continuing the analogy, I can of course plug in a second USB dongle that operates in a different band, and again the USB dongle may be appropriately certified.
However this discussion may be hypothetical because for it to have any practical relevance a suitable M.2 card must exist !