Is a toy's remote controller interchangeable?
The original solution for the 27MHz band was different crystals (matched sender and receiver): http://www.ukrcc.org/27mhz.html

The ISM bands (433 / 915MHz) tend to use digital code switching, your option 2. The number of codes is usually small and may be selectable by a switch somewhere. This makes it straightforward to buy replacement remotes.

The 2.4GHz band is used by all kinds of protocols. Some of the pricier quadcopters define their own WiFi hotspot for control and telemetry; WiFi has both 13 different sub-bands and a coding system (SSID).