House Rules

Setting
Toss out almost everything about the Order of Hermes as listed in Against the Dark: The Transylvanian Tribunal. Unless your character is from the Tribunal itself, most of its workings are shrouded in mystery, as intended by House Tremere, who rule the majority of the covenants in the Tribunal.

History
Forget anything about Hermetic history, and world history, after 1200 BCE. Your characters may have enormous impact, or none at all. Nothing is cast in stone.

Canonical Sources
All 5th edition Ars Magica books are considered canonical, in terms of rules. Anything about history may be considered to be the accepted story, though the actual truth may differ. Only Against the Dark is considered non-canonical, in terms of Hermetic history.

System Changes
Laboratory Texts (ArM 5e, pg. 102): Writing laboratory texts is changed to (Latin + Communication) x 20 levels per season.