まだObjective-Cなんかやってんのかよーという声も聞こえてきそうですが、
Objective-CでSegueを使って遷移する時に超便利なカテゴリーを今回は紹介します！

UIViewController+SegueBlock.h

#import <UIKit/UIKit.h>

typedef void (^SegueBlock) (UIStoryboardSegue *segue);


@interface UIViewController (SegueBlock)

- (void)performSegueWithIdentifier:(NSString *)segue sender:(id)sender block:(SegueBlock)block;

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender NS_REQUIRES_SUPER;

@end

UIViewController+SegueBlock.m

#import "UIViewController+SegueBlock.h"
#import <objc/runtime.h>


@implementation UIViewController (SegueBlock)

- (void)performSegueWithIdentifier:(NSString *)segue sender:(id)sender block:(SegueBlock)block
{
    objc_setAssociatedObject(self, _cmd, block, OBJC_ASSOCIATION_RETAIN);
    [self performSegueWithIdentifier:segue sender:sender];
}

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wobjc-protocol-method-implementation"
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender NS_REQUIRES_SUPER

{
    if ([self segueBlock]) {
        [self segueBlock] (segue);
    }
    
    objc_setAssociatedObject(self, @selector(performSegueWithIdentifier:sender:block:), nil, OBJC_ASSOCIATION_RETAIN);
}
#pragma clang diagnostic pop

- (SegueBlock)segueBlock
{
    return objc_getAssociatedObject(self, @selector(performSegueWithIdentifier:sender:block:));
}

@end

使用例

ViewController.m

- (IBAction)showSecondViewControllerButton:(UIButton *)sender {
    [self performSegueWithIdentifier:@"showSecondViewControler" sender:nil block:^(UIStoryboardSegue *segue) {
        SecondViewController *secondViewController =segue.destinationViewController;
        secondViewController.labelText = @"segueのブロックで値渡し";
    }];
}

// 以下のメソッドを実装する場合は Super でメソッドを呼ぶ
//- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
//{
//    [super prepareForSegue:segue sender:sender];
//}

@end

ブロックでdestinationViewControllerを取得できるので
次のViewControllerに値やオブジェクトを渡す時にかなり便利になります！

Githubにソースコードを上げてます。
SegueSample-GitHub