according to the apple app store guidelines:
"Apps that do not use system provided items, such as buttons and icons, correctly and as described in the Apple iOS Human Interface Guidelines may be rejected"
https://developer.apple.com/appstore/resources/approval/guidelines.html
here is how you add icons in xcode 4.6.3 http://wpguru.co.uk/2013/09/how-to-add-ios-7-icons-in-xcode-4-6-3/