Can concurrence type be changed of NSPersistentDocument's managedObjectContext?

I need the concurrence type of NSPersistentDocument's managedObjectContext to be NSMainQueueConcurrencyType because I need contexts in other threads.

Yes, you were right. Overriding manageObjectContext you can modify concurrency type. Maybe, I have some mistakes.

 - (NSManagedObjectContext *)managedObjectContext {
    __strong static NSManagedObjectContext *myManagedObjectContext = nil;

    if (myManagedObjectContext == nil) {
        myManagedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];

        NSPersistentStoreCoordinator *psc = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
        [myManagedObjectContext setPersistentStoreCoordinator:psc];
    }

    return myManagedObjectContext;
}