Also I should note now that it's all over with:
the 100% accurate Massacre actually occured in two waves, not a general massacre as I chose to depict for dramatic/truncation purposes. Overnight, Coligny and other leading Protestants -- both prominent townsmen and noble leftovers from the royal marriage -- were assassinated.
It wasn't until midday on the 24th, prompted by the miraculous blooming of a hawthorn bush (perhaps a common signifier of both divine and demonic intervention in early modern France, see its relevance during the 1630s Possession at Loudun) in a cemetary adjacent to the site of the contentious Gastines Cross, that the general Catholic population turned on their Calvinist neighbors.
It's unclear whether or not the plotters intended for this to happen, but it was likely met with some mix of satisfaction and disgust -- King Charles' laugh-cry fits as alluded to by Alexandre/Henri III are historically-attested and probably encapsulate the mood somewhat. As for the plotters themselves: it could've been any combination of some or all of the Royal family, certainly some Guise affiliates, and perhaps with prodding from the Italian contingency at court. We'll never quite know.
French royal proclamations struggled with the legality of all that transpired. I can't be bothered to pull the exact sources but the wording is wonky and generally can be interpreted as "We disavow this awful massacre but maybe it was good and had to happen? There were some real traitors in that corpse pile after all."