No. The closest is the Geneva conventions which holds that false flag opperations are not war crimes, but does not offer protections to belligerents captured while conducting such operations (You specifically need to be in an identifiable uniform, openly carrying arms, and operating within the bounds of international rules of war, and following a chain of command for war prisoner status to be granted).
Failing that, you operate under color of law of the nation you are spying for, and they're laws are usually sufficient to cover prosecution of various false flag operators (and there aren't any conventions on ordinary law during war, so you can be more brutal than if they were a uniformed enemy soldier). Laws against Impersonating an officer, espionage, treachery and sedition, and sabotage are usually sufficient for a criminal court to hold hearings on.
Most Conventions on War actually do not ban practices for internal use only. For example, chemical warfar is a war crime. You cannot use tear gas on the enemy encampments. But you are more than free to spray tear gas on the unruly civilian war protestors in your capital... or your own troops so they know what to do in case the enemy decides to get it some war crimes charges in the aftermath. You can't torture anyone on the enemies side (civilians or otherwise) but you can torture your own soldiers for failing you for the last time as much as you want. You also cannot kill surrendered enemy troops or troops who are incapable of fighting... you're own men you can kill because you haven't killed an underling in 2 hours. Even Vader follows this rule (In episode 4, he's questioning a rebel troop on the ship, but doesn't kill him. He saves force choking for his own admirals who mess up or know not the power of the force).
This is why Mission Impossible tells it's spys "If discovered, all knowledge of your activities will be disavowed." It's because the boss is telling it's agent that the agent's mission is one that if the enemy captures you, your own your own and you won't have Geneva POW protections because we are not going to war over you. Enjoy your trip to Moscow! (This is better discussed in Star Trek: TNG episode "Chains of Command" where Picard is ordered by Star Fleet to infiltrate the Cardassian Union and is captured... because the Federation and Star Fleet publicly do not want a war with Cardassia, when they are confronted by the Cardassian government, they deny any knowledge that Picard was operating under orders. If they don't deny it, they admit to an act of war against Cardassia... but if they do, Picard is not protected as a prisoner of war since officially no one ordered him to do this (even if war breaks out)... which means he is subject to the laws of Cardassia. And just so we're clear on what that legal system is like, In the Cardassian Justice System, the people are represented by two distinct entities: The State which infallibly pronunces you guilty, and the courts, which give you a chance to confess and let your family denounce you to save face. (Doing Doing). Nothing says they can torture Picard, but more importantly, nothing says they can't... and they do so love to do it. Especially when you can't count the number of lights... they seem to relish their inability to understand how wrong you are.
Suffice to say, it's a job one should never take lightly when tasked to do (and in China's case, you aren't even asked to do it.).