Bulk Changing Application Icons on System
@klanomath is close, but you actually can bulk change the icon. While the .icns file is stored within the application, it's referenced in an .xml file known as info.plist inside the Contents folder of every app. There's a string CFBundleIconFile with specifies the name of the .icns file inside the Resources folder.

While simply finding every .icns file and changing it would probably work in most cases, it's not the best practice. While it's rare for .icns files to be used for anything other than application icons, some app bundles include multiple side apps. This method minimizes risk.

If you'd like, I'll gladly assist in building an app to fit your renaming needs.