1 is possible. You can create an empty device that you can just use to generate credentials to send data via our cloud. This is free for now, but we may start charging in the future.
2 is also possible but would require some reprogramming to set the APN.
Is possible for sending device data (but you lose your ability to remotely control devices, perform over-the-air (OTA) firmware updates, etc.). So, some limited functionality can work.
As Reuben said, that would require firmware reprogramming.