The Syrrannite Reformation was an event that occured in Vulcan history and resulted in the removal of Administrator V'Las from his position.

In an alternate timeline where the United Earth never joined the Coalition of Planets, Vulcan ambassador Sarek explained to James T. Kirk that there were numerous changes in the Vulcan High Command after the Syrrannite Reformation. However, Kirk was unaware of what the reformation was at the time. (TOS novel: A Less Perfect Union)

Presumably, this refers to the action of the Syrrannites who removed V'Las from power and returned Surak's teachings to the Vulcan people.