> it's almost mandated by law that there can't be. FCC regulations require that devices be made resistant to attempts to change their function in an effort to limit people's ability to transmit stuff unintentionally (or intentionally). Modern radio protocols are heavily dependent on SDR (software defined radio), so fixed function is probably infeasible. You could make the firmware unchangeable, but now any bugs discovered in your public source code are now entirely uncorrectable.
1. You can use signed firmwares to make it both compliant and upgradable.
2. You can separate the controller/receiver and the transmitter, and only lock up/restrict the transmitter part.
Alternatively, you can implement the restriction at the hardware level if feasible (effectively making it fixed function).
3. Finally, you can sell the parts individually to serve a separate market segment.
1. You can use signed firmwares to make it both compliant and upgradable.
2. You can separate the controller/receiver and the transmitter, and only lock up/restrict the transmitter part. Alternatively, you can implement the restriction at the hardware level if feasible (effectively making it fixed function).
3. Finally, you can sell the parts individually to serve a separate market segment.