Thank you!
The Ars Magica Guide will contain a history of the order until 1507 and ideas about how different factions in the order deal with the political situation in the Magical Renaissance.
The "discovery" of the Americas will play a role, as does the position of the Church towards magic.
Note:
In my Ars Magica world – shaped in the early 90s – the order and magic was always in full hiding from society and the church, as was everyone with fae blood or with supernatural powers. My first book (for 5e) is also based on the assumption. No mage would ever show his powers in public and no human with fae blood would ever admit to that. Even the DnD version of our books is based on such principles.
However: an "alternative history" - the Magical Renaissance – is created when the leader of Florence, Lorenzo de’ Medici, does not die in 1492. In this world, magicians and humans with special powers make baby steps into the light of of society. Carefully...
Here is a part of our chronology:
1492
Florence: A group of Florentine citizens uncover a heinous plot to assassinate Lorenzo de’ Medici and the Magnificent is healed by Divine intervention. It is said that his saviors had to go through Heaven and Hell to uncover a plot and find the instrument by which they could conquer the forces of Hell. (Events from "The Straight Way Lost", our first book.) News breaks that they used powerful magics and were supported by brave individuals from non-human lineages that have long shared the earth with mankind. Before this revelation, non-humans had been hiding for ages and only "white magic" through divine intervention was officially accepted. Now, society has to absorb this news.
An excerpt of our detailed chapter about how different parts of the society react to such news and how factions in the world build.
Reaction of the Catholic Church:
Most higher Church officials had already known about the existence of other species, and there have always been individuals with fae-blood within the ranks of the church.
This – and the fact that the Church would not want to be believed as ignorant – leads to a very fast official reaction by the Pope. On January 1, 1493, the newly elected Pope Alexander VI, Rodrigo Borgia, issues the papal bull "Sunt aliae gentes" which declares that there was never a doubt about the existence of other species, but that a great confusion has overcome some members of the flock. This is why the Church elaborates that God loves all of his children and that all who obey Christian dogma are allowed to enter Paradise. The letter also assures that humans hold a special place in God’s kingdom, as they are his firstborn on earth.
This papal bull does not go unopposed, in particular as it comes from a widely unpopular Spanish Pope. Many amongst the higher ranks protest, but Borgia silences them with bribes or threats. There are, however, a few fractions opposed to the equal status of non-human-species. Read the section about the religious orders below.
When Alexander dies in 1503, he is followed by Francesco Todeschini Piccolomini, who styles himself Pius III. The nephew of the pious and educated Pius II is a half-elf (DnD) of a renowned noble family, and openly declares his family-connections after the papal bull is published.
Only a few weeks after his election, there is an attempt on his life. Some say, that the mighty Cardinal Francesco della Rovere conspired with the Puri to take the office for himself. Others believe that the Dominican order is behind this poisoning. Since then, Pius is never seen without his personal guards, a taster and his private physician – who is suspected to be a magical healer.
So... this is part of our official history in the main book.
In the Ars Magica conversion guide, we will discuss alternative views or way how the order will react to such news and how it might change the order. (That is already changed from its medieval form on which we also will offer views.)
But: these will always only be options: Every SG can decide to open the society to more or less magic. 
