Available in any patch, for all games, posted after this message.
EvalLoyalty = <Operator>;<Value>
Operator: One of <, >, <=, >=, =, DICE
Apply on the currently selected region.
If you want to have an event which triggers if the loyalty of X regions are above or under a value, just use one EvalLoyalty command per region (one per line).
If you want to have an event which triggers if region X or region Y satisfies a criteria, you have to make 2 events, either one activating a third event, which is the one doing the in-game effect.
EvalControl works the same, but for military control.