First close your Xcode and backup the iPhoneOS.platform Info.plist by running this in Mac Terminal
sudo cp -p /Developer/Platforms/iPhoneOS.platform/Info.plist /Developer/Platforms/iPhoneOS.platform/Info.plist.bak
Then edit the iPhoneOS.platform Info.plist file
sudo vi /Developer/Platforms/iPhoneOS.platform/Info.plist
Launch Xcode and then create new project using my Xcode Template for pwned device "View-Based Application" to build and go to either Project Settings 2.0 or Project Settings 2.1 or iPhone Simulator and you don't need the trick to reset it anymore.
Remember, you still need a fake codesign identity and patched MobileInstallation binary in your iPhone.
If you are registered iPhone Developer with provisioning profile and codesign cert from Apple, please remember to revert the PhoneOS.platform Info.plist back to the original one before building your project to App Store.
If you have "security policy error" after Build & Go. Do these steps
(1) Install a new free app from App Store in iPhone (not sync from iTunes)
(2) Launch that newly purchased free app and then close it.
(3) Reboot your iPhone (that is power off and on again)
(4) Launch the app again that you have Build & Go in Xcode to iPhone.
Please also refer to the latest article for SDK2.2.1