You can put up essentially the same app, as long as it is obvious it is a different app. Which means you're fighting trademark law, not copyright.
Change the icon, change the name, change the publisher name, and change the about us page, and you've done enough.
Think FireFox vs IceWeasel.
Furthermore - if someone takes your GPL'd app (which, presumably, you own the registered trademark for?) and puts it up on the AppStore, Apple will enforce your trademark and kick them off once you bring it to their attention.
If you don't own your trademark, then you have to do the above changes, _register_ the trademark, and then resubmit.