Apparently a polish carrier called Multimedia has recently introduced a new, revolutionary service for some customers. It's called "set up a custom wi-fi configuration", and it's just 5 pln (a little over $1)! It lets you think up of a ssid and password, and configure your router to use those! That's an amazing invention, isn't it? /s
Some customers apparently have absolutely no access to their routers, not even to the web interface, and they can't use their own either. All reconfiguration must be done through the customer service portal or by phone. That means the carrier can change for every little thing, including changing the Wi-Fi config! I'm not sure if you can even bridge, but I guess not. Note that this does not affect all customers of that carrier, just a minority.
Daisy-chaining routers is can severely degrade some services (gaming, p2p) due to NAT. Assuming the ISP-provided one supports PCP or UPnP-IGD you need a client on your own router that relays port forwarding configuration to the upstream router. This is possible but may need non-trival setup.
Some customers apparently have absolutely no access to their routers, not even to the web interface, and they can't use their own either. All reconfiguration must be done through the customer service portal or by phone. That means the carrier can change for every little thing, including changing the Wi-Fi config! I'm not sure if you can even bridge, but I guess not. Note that this does not affect all customers of that carrier, just a minority.