Assassinating Iranian Major General Qaseem Soleimani was a justified act. But it took place within the context of a largely unjust and strategically indefensible grand strategy, so it is unlikely to be a net positive in the long run.
Two Christian schools of thought might support covert operations and espionage: the just war tradition and a kind of “dirty hands” moralism. The dirty hands view says all those in political power must unavoidably resort to evil for the common good. The just war tradition has a different approach.