Okay, it appears there's a single 15A fuse on the entire "stop light" (Japanese term for "brake light"?) circuitry, which is far more complex than a simple old brake light circuit on most older cars. From the diagrams below you can see that it is indeed tied into several control module and relay assemblies, including the main body ECU that talks to the ignition.
So once we get past the relative complexity of the circuit, this is actually a good thing, as it allows us to kill just the portion of the circuit we want (that which allows the ignition to fire) without affecting anything else (in theory anyway). This means even if the switch failed or was accidentally flipped during driving, brake lights and everything SHOULD still operate as normal. It also means the switch will be under less load, since it's only switching a small portion of the circuit, instead of the entire thing.
I'll have to spend a bit more time with these diagrams, but it appears that switching the wire circled in red would interrupt the brake signal from the "Stop Light Switch Assembly" to the Main Body ECU, while leaving all other circuits linked to the "Stop Light Switch Assembly" (including brake lights themselves) unaffected. The blue circled wire appears to be the output controlling the relay for the brake lights and the "BRK LP Relay" linked to the ignition, but if the ECU never receives a signal from the "Stop Light Switch Assembly" it shouldn't matter....the ignition won't fire, even if the BRK LP Relay is closed and ready to go.
Looking at the first and third diagram, you can see that the ECM also talks with this circuit, and with the "Stop Light" switch closed, the ECM is also able to trigger the BRK LP Relay....but if the ECU controls the IGN signal, again, it shouldn't matter. As long as the ECU doesn't see a brake signal, it shouldn't be able to start.
It's worth noting to anyone else considering this method in the future, that while my amateur assessment of this is that it would be perfectly safe, and I can't imagine how a slight change to a relatively unimportant circuit would have any major effect on critical vehicle systems or safety (other than the intended affect of not allowing the vehicle to start when the kill switch is open), these are complex systems involving computers and proprietary "black box" logic, so take this all with a grain of salt and CAVEAT EMPTOR. At the very least, this SHOULD (in theory) have NO MORE effect than pulling the brake light fuse, which would kill this ENTIRE circuit, not just a small portion of it. But, again, I'm just some amateur idiot on a forum, so CAVEAT EMPTOR!!!
I'll check out these diagrams and the FSM a bit more, and If this is the route I go, I'll report back with testing results. Thanks
@LXRuth !