Hello.
The main difference between Passthrough and Bridge is that in Passthrough, the router's DHCP Server still works and the regular LAN interface is still up, allowing clients to connect to the router's local network as usual, while Bridge mode disables all of these features and simply gives the a single specified device its WAN IP address.
More information:
https://wiki.teltonika-networks.com/view/RUT955_Mobile#Passthrough_mode
Can one of the two send sms commands to RUT955 to change profiles? Could you access the RUT955 website to manage it and with which IP address?
Please, describe in more detail what you want to achieve?
Best regards.