The CBT does not affect the spark side of the system.
It works by sequentially shutting off injectors to see what the effect of a known cylinder drop-out has on the overall performance of the engine while it is under test.
This makes the whole discussion about shorting out the ignition moot.
Getting back to the original problem, a #6 injector is unlikely to cause a P0302 misfire code.
I'd vote against the dealership's diagnosis.
Steve
