As far as firing while cloaked, "Face of the Enemy" seemed to confirm the notion that the cloak has to be carefully regulated to prevent any stray emissions from leaking out and being detectable. I seem to recall that something similar was suggested in "Tin Man" when the first warbird was pushing its engines so hard the Enterprise could detect it briefly, but I'd have to check the transcript and see what the dialogue says. I always got the impression from TUC that Chang's prototype (Dakronh
) traded the ability to fire while cloaked for being more vulnerable while the ship was maneuvering in combat and generating more "tailpipe" waste. The novelization states that the Enterprise's torpedo systems generate a neutron surge while active, making the reader wonder if the assassins could actually access that system to attack Kronos One. This also gives more context to Chekov's line that only another ship could produce a neutron surge "that large."