WDUK

Here's what you do!

1. Terminal: Unzip the ipa (it's just a zip file after all)
  unzip -q App.ipa
  
1a, You will need to have the entitlements file, this information is needed during signing.
  codesign -d --entitlements :- "Payload/App.app"
  
2. Terminal: This will produce a `Payload/` directory. Remove the existing code signature.
  rm -rf Payload/App.app/_CodeSignature

WDUK

Have a developer account?
Want to run GBA4iOS 2.0 without needing to change your device date all the time?
Here's what you do!

1. Safari: Download the ipa file direct
  http://gba4iosapp.com/download/GBA4iOS.ipa
  
2. Terminal: Unzip the ipa (it's just a zip file after all)
  unzip -q GBA4iOS.ipa