Briefly:
With the 'affair of the Placards', a seemingly powerless group without appreciable assets transformed France. Unfortunately, it appears the author, Antoine Marcourt, didn't really understand what he was doing and by the time the consequences were fully apparent a savage civil war had taken place and Protestantism had been obliterated in France.
The challenge is to think of ways to avoid this fiasco and the wars that followed. Bonus marks if the method requires resources not much greater than the agitators employed historically.
Boring version:
Since its earliest days, the Catholic church was no stranger to heresy and it took centuries for it to iron out its doctrines to a degree sufficient to prevent endemic sectarian conflict. Historians tend to blame the stultification of the late classical and early medieval periods on the rigid theology that resulted.
Sufficiently agile thinkers were always able to find a way out of the straitjacket, however. The need to synthesise religious and secular law provided experience in one technique valuable to this process and even in the darkest of the dark ages this was an everyday necessity for lawyers. Synthesis, together with the magical word 'if', enabled skilful (or cynical) thinkers to make the most outrageous suggestions without actually committing heresy. This is why Copernicus was able not only to evade prosecution but also to circulate his work all over Europe.
Thinkers of this sort had assembled at Meaux decades before Luther nailed his thesis to the church door and continued to do so without interference for years afterwards. Even when they were forced to move by the courts, they only decamped to the hospitality of Marguerite d'Angoulême (also of Navarre), King Francois I's sister. This was hardly severe punishment.
All that changed with the affair of the Placards. In the early hours of 18 October 1534, inflammatory posters were erected all over France attacking "the horrible, gross and insufferable abuses of the papal mass" and claiming that priests "have seized, destroyed, and swallowed up everything; they have disinherited kings, princes, nobles, merchants, and everyone else imaginable". Supposedly a copy was nailed to the door of the King's bedchamber.
To attack the papacy was one thing but dragging the King into it was another. Within weeks a half-dozen heretics had been burned. In mid-January a spectacular procession was organised in which the King, with representatives of every civic group imaginable dragged along, paraded holy relics through the streets prior to the execution of another six heretics. But such scenes were mundane compared with the spectacular violence of the following half-century.
The fiasco wasn't unforeseeable. The church and state would tolerate cautious theological experimentation but not anything that challenged the social order. All someone wishing to stir up conflict needed to do was to challenge their authority and the response would be predictable. This objective was within reach of large numbers of people.
Metaphorically speaking, it's easy for Gavrilo Princip to pitch Europe into chaos but how is he to bring peace and harmony to the continent? Things weren't completely hopeless. Theodore Beza, a prominent Calvinist, lamented that "everything was shattered by the indiscreet zeal of a few" and decried the posters' "sharp and violent style". How could people like Beza and enough moderate Catholics be brought together to create a political accommodation?