[Al Skierkiewicz]

Jeffrey,
I should have answered this earlier. The 20 amp breaker rule requires that you use #18 to feed your custom circuit. However, you may add a smaller fuse to the custom circuit if you feel it is appropriate.

F. Custom circuits and sensors powered via the cRIO-FRC or the Digital Sidecar are protected by the breaker on the circuit(s) supplying those devices. Power feeds to all other custom circuits must be protected with a dedicated 20-amp circuit breaker on the PD Board.

In addition to the required branch power circuit breakers, smaller value fuses or breakers may be incorporated into custom circuits for additional protection.
No one expects that wiring on a custom circuit board be #18. Common electrical practice would suggest that a 1 amp fuse would protect anything on the board that is wired with smaller gauge wire. LEDs for instance are rarely wired with #18 gauge wire.