I am trying to run Xcode 6.4 on El Capitan and I can run with the instructions on this post.
But I am looking for a way to run it without any external program as I r
There are two places in Exceptions.plist which list Xcode. The one you don't have listed is:
com.apple.Xcode AppStoreIdentifier 497799835 AppStoreUpdateIsFree HardDisabled HighVersion 5085.0
It is necessary to re-install Xcode afterwards.