gistfile1.m

    // navigation bar の背景画像を設定
    [[UINavigationBar appearance] setBackgroundImage:[UIImage imageNamed:@"navigationbar.png"]
                                       forBarMetrics:UIBarMetricsDefault];
    
    UIImage *backButtonImage = [[UIImage imageNamed:@"back.png"] resizableImageWithCapInsets:UIEdgeInsetsMake(0, 28, 0, 0)];
    
    [[UIBarButtonItem appearance] setBackButtonBackgroundImage:backButtonImage
                                           forState:UIControlStateNormal
                                         barMetrics:UIBarMetricsDefault];
    [[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:UIOffsetMake(-100, 0)
                                              forBarMetrics:UIBarMetricsDefault];
    
    // Setting UIViewController
    [UIViewController setDefaultSettingWithBlock:^(UIViewController *viewController) {
        UIBarButtonItem *backBarButtonItem;
        backBarButtonItem = viewController.navigationItem.backBarButtonItem;
        if (!backBarButtonItem) {
            backBarButtonItem = [UIBarButtonItem new];
            [viewController.navigationItem setBackBarButtonItem:backBarButtonItem];
        }
        [backBarButtonItem setBackButtonBackgroundImage:backButtonImage
                                               forState:UIControlStateNormal
                                             barMetrics:UIBarMetricsDefault];
        [backBarButtonItem setBackButtonTitlePositionAdjustment:UIOffsetMake(-100, 0)
                                                  forBarMetrics:UIBarMetricsDefault];
        
        // 背景画像を設定
        UIImage *bgImage = [UIImage imageNamed:@"background.png"];
        viewController.view.backgroundColor = [UIColor colorWithPatternImage:bgImage];
    }];

gistfile2.txt

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

@implementation UIViewController (DefaultSetting)
static void (^settingHandler)(UIViewController *viewController);
+ (void)setDefaultSettingWithBlock:(void (^)(UIViewController* viewController))handler
{
    settingHandler = handler;
    SEL originalSelector = @selector(viewDidLoad);
    SEL overrideSelector = @selector(swizz_viewDidLoad);
    
    Method originalMethod = class_getInstanceMethod(self, originalSelector);
    Method overrideMethod = class_getInstanceMethod(self, overrideSelector);
    
    method_exchangeImplementations(originalMethod, overrideMethod);
}

- (void)swizz_viewDidLoad
{
    [self swizz_viewDidLoad]; //swizz_* was renamed by method_exchangeImplementations()
    settingHandler(self);
}
@end