The original LEGO Mindstorms did something similar. In order to upload firmware to the RCX brick (a common operation, since the firmware was stored in volatile RAM) you had to pass a "copyrighted unlock string" ("Do you byte, when I knock?") which would be verified by both the interface DLL and the boot ROM itself.

The intent was apparently to use the copyright on that phrase as a means to force developers to use the officially sanctioned API. I don't know if that was ever legally enforceable; it certainly didn't stop hobbyists from plugging the unlock string into their code.