As far as I know, nothing quite like this exists in canon. The Jedi certainly aren't shy about undercover operations (and we see at least one such assignment in The Clone Wars cartoon), or with occasionally working with bounty hunters and pirates, but ordinarily they don't "become the mask"1 and engage in more distasteful criminal endeavours.
However, the canon novel Dark Disciple gives us one possible example, and the closest I can think of in the new canon:
Master Quinlan Vos
Vos specializes in deep cover assignments in organized crime rings, which forces him to do some damned distasteful things in the line of duty; however, the canon novel Dark Disciple is slightly unique, because the Jedi Council orders him to assassinate Count Dooku:
"A course of action that we reluctantly deemed necessary" said Mace. Vos's gaze flickered to Yoda, doubtless curious as to why Windu spoke instead of the head of the Council. "There's no way to phrase this other than bluntly. Master Vos — the Council wants you to assassinate Count Dooku."
Dark Disciple Chapter 3
Although he isn't trained (by the Jedi) in the use of Dark Side techniques, he and his partner on the mission (Asajj Ventress) agree that tapping into the Dark Side is the only way for him to be strong enough to stand a chance, and he goes far enough along that path to kill an innocent creature, the last of its kind:
Vos drew in great, ragged gulps of air, his body straining with tension. He heard Ventress's voice shouting at him, "What are you waiting for? Kill it, Vos!"
"Ventress," he called, still controlling the Sleeper, "it may be the last of its kind!"
He made his choice.
He focused on his earlier fear: the helplessness he had felt, and his anger at it. He narrowed his eyes, calling up the hatred and rage, feeling them burst into him, white-hot and so very powerful.
This was an enemy. This was Count Dooku. Vos extended his hand, slowly, deliberately, taking the time to truly experience the emotions as they translated from thought to action.
Dark Disciple Chapter 17
Without wishing to spoil the rest of the novel, this turns out to be an astonishingly bad plan, and the Jedi Council quickly comes to regret following through with it.
1 TVTropes link; it's dangerous to go alone