I think that you will have to try to get info using AT commands to get that info from the USB LTE modem, if you use two different USB LTE Modems there is a way to read the IMEI (usb dongle Serial Number), I think it is possible to read SIM ID too...
The signal strengt is also possisble to read, but I am not sure about the signal mode (LTE vs UTMS) probably that data is available too.
In that way you could make a script to check for that and replace the config file contents. other way it to create a simple page using php or cgi with two buttons and do it manually, you will have to write those scripts to put one or another config anyway, and the two buttons is easy to do...