[Justin Stiltner]

R43 Blue box

"
Smaller value Snap Action auto resetting breakers may be used on the PD Board for circuitry not defined above.

In addition to the required branch power circuit breakers, smaller value fuses or breakers may be incorporated into custom circuits for additional protection.
"

So you may use a 20A breaker, or substitute a smaller one, but it must be the same make, model, etc of the ones included in the kit.

Personally, I would use a 20A that you already have, and put a fuse inline if you are worried about trying to protect your device. In reality I have never seen a fuse protect a device that was miswired, unless that device had a crowbar circuit built in.