Hi,
I'm coming with additional information that could help you.
You CAN swap the modems of the product, but you would need a half of other product's version PCB (the one that has modem soldered in).
You should be able to connect them and have the modem and combined router operational without any additional changes.
How are you going to get that half of the PCB is another question, but that's the way it could be done and achieved.
EB.