Right, finally got rid of that customer and on a break...
- Monthly rituals like site searching: Start from the province with the lowest province number that you have not done yet (and in the case of site searching spells, that does not have more than 1 site already found AND does not have that path searched at any level). This cannot be altered.
- Actions in combat: Always performed in the order the commanders appear in the army setup, from top to bottom. This is because each commander has the invisible unique identifier, which is used to keep track of experience, magic paths, afflictions etc that are specific to the individual unit. Lowest number goes first.
- Random events: Not determined by province number, but number of events is capped at 3. If you have a number of turmoil/misfortune provinces you just captured, be prepared to deal with the fallout from that. However, it is possible that events are checked for each province every turn and if so, it probably goes from lowest up. So your specific situation may casue problems. Not necessarily feasible to change this mechanism.
- Globals: Lowest ID goes first. Most powerful spell will override weakest active one in case this results in a clash (assuming it's stronger than the weakest active one, otherwise it fizzles).
- Artifacts: Lowest number goes first
The ritual casting order should be random according to the manual, but a random casting order has never to my knowledge been observed. Combat is verified to go in IUID order, not randomly.