Javassist. Какова основная идея и где реальное использование?

Я обновил код Брайана для моей Sierra iMac:

# this version was tested OK vith macOs Sierra 10.12.5 (16F73) on oct 0th, 2017
# original ipa file must be store in current working directory 

IPA="ipa-filename.ipa"
PROVISION="path-to.mobileprovision"
CERTIFICATE="hexadecimal-certificate-identifier" # must be in keychain

# unzip the ipa
unzip -q "$IPA"

# remove the signature
rm -rf Payload/*.app/_CodeSignature

# replace the provision
cp "$PROVISION" Payload/*.app/embedded.mobileprovision

# generate entitlements for current app
cd Payload/
codesign -d --entitlements - *.app > entitlements.plist
cd ..
mv Payload/entitlements.plist entitlements.plist

# sign with the new certificate and entitlements
/usr/bin/codesign -f -s "$CERTIFICATE" '--entitlements' 'entitlements.plist'  Payload/*.app

# zip it back up
zip -qr resigned.ipa Payload