NSManagedObject *object = ...;
[object setValue:@"test" forKey: @"test"];
[[RKObjectManager sharedManager] postObject:object 
                                 parameters:nil 
                                    success:^(RKObjectRequestOperation *operation,RKMappingResult *mappingResult) { NSLog(@"success,nothing to do"); }
                                    failure:^(RKObjectRequestOperation *operation,NSError *error) { 
  // I want to discard changes made to object here 
}

更新：RestKit 0.20