Does the distribution of Xcode now available from the OS X App Store replace a previous version downloaded directly from the Apple Developer site; or will "switching" from an Apple Developer installation to an App Store installation cause problems?
You really shouldn't have any problems switching from an installed 4.2 to a Mac App Store "installed" 4.3. All your profiles are stored in ~/Library. All your certificates are in your keychain.
I've switched fully to 4.3 and not had a problem with any configuration. It's all still working just as it was in 4.2.
That said, if you do have specific problems, then please either open a new question for that specific problem or file a radar if it's something that Apple need to fix.
来源：https://stackoverflow.com/questions/9672209/does-the-app-store-version-of-xcode-cleanly-replace-the-non-app-store-version