Здесь есть отличное руководство по новым функциям настройки в iOS 5: http://www.raywenderlich.com/4344/user-interface-customization-in-ios-5
Вот копия кода с этого сайта, которая имеет дело с настройкой UIBarButtonItems, это довольно очевидно:
UIImage *button30 = [[UIImage imageNamed:@"button_textured_30"] resizableImageWithCapInsets:UIEdgeInsetsMake(0, 5, 0, 5)];
UIImage *button24 = [[UIImage imageNamed:@"button_textured_24"] resizableImageWithCapInsets:UIEdgeInsetsMake(0, 5, 0, 5)];
[[UIBarButtonItem appearance] setBackgroundImage:button30 forState:UIControlStateNormal
barMetrics:UIBarMetricsDefault];
[[UIBarButtonItem appearance] setBackgroundImage:button24 forState:UIControlStateNormal
barMetrics:UIBarMetricsLandscapePhone];
[[UIBarButtonItem appearance] setTitleTextAttributes:
[NSDictionary dictionaryWithObjectsAndKeys:
[UIColor colorWithRed:220.0/255.0 green:104.0/255.0 blue:1.0/255.0 alpha:1.0],
UITextAttributeTextColor,
[UIColor colorWithRed:1.0 green:1.0 blue:1.0 alpha:1.0],
UITextAttributeTextShadowColor,
[NSValue valueWithUIOffset:UIOffsetMake(0, 1)],
UITextAttributeTextShadowOffset,
[UIFont fontWithName:@"AmericanTypewriter" size:0.0],
UITextAttributeFont,
nil]
forState:UIControlStateNormal];