Finally figured out how to it exactly the way I was wanting to. The “Set Collision Enabled” function node is the key. So I left my Generate Overlap Events for the box collision component of my BP set to on, but then implemented that function. With it you can set the specific status of collisions for the referenced object. So I set one of these to No Collision and attached that to my EventBeginPlay scripts, then I set another to Query Only and attached that to my Custom Event, the latter activating collisions for the box collision component.
Basically, now when the game starts, collisions are possible but automatically turned off by my EventBeginPlay. Then, when I interact with the Circuit Breaker BP, my BP Interface sends a message to the Circuit Breaker BP to execute, which in turn sends a message to my Custom Event on the Doors BP to execute, which in turn changes the collision status on so that when I return to the doors they’ll open as scripted to.
Funny how knowing the single correct function node to use can be the key to unlocking everything, right?