Interface Builder iPhone iPad simulated interface elements

When you create the Interface Builder file in xcode, you are asked to create it for the iPhone or iPad. That is not only the question for the screen dimmensions at start up, but also is important to properly displaying the navi开发者_如何学运维gation bar - custom colors, as well tables and so on.

Is there any way to change the iPhone/iPad format in the existing Interface Builder file?

I'm not quite sure I understand your question but there are two things you can look at:
- (in IB) Under File you can Create an iPad Version of an iPhone view and Create an iPhone/iPod Touch version of an iPad view
- .xib files are text files, so you can open them up with an editor and modify them