Function apply_plan_change 

pub fn apply_plan_change(
    plan: &mut Plan,
    actor: ActorId,
    proposed: &Plan,
    reason: impl Into<String>,
    timestamp: DateTime<Utc>,
    id: OperationId,
) -> Result<Operation, EngineError>

Apply a reviewed full proposal as one delta operation.

The actor and reason are checked before the proposal is compared, as the command itself checks them first, so every refusal is the one applying the full proposal would produce.