The anatomy of a macOS application

When Mac OS X was designed, it switched to the bundle structure inherited from NeXTSTEP. Instead of this multitude of resources, apps consisted of a hierarchy of directories containing files of executable code, and those with what had in Mac OS been supporting resources. Those app bundles came to adopt a standard form, shown below.
↫ Howard Oakley

A short, but nonetheless informative overview of the structure of a macOS application. I’m sure most people on OSNews are aware that a macOS application is a bundle, which is effectively a glorified directory containing a variety of files and subdirectories that together make up the application. I haven’t used macOS in a while, but I think you can right-click on an application and open it as a folder to dig around inside of it.

I’m trying to remember from my days as a Mac OS X user – 15-20 years ago – if there was ever a real need to do so, but I’m sure there were a few hacks you could do by messing around with the files inside of application bundles. These days, perhaps with all the code-signing, phoning-home to Apple, and other security trickery going on, such acts are quite frowned upon. Does making any otherwise harmless changes inside an application bundle set off a ton of alarm bells in macOs these days?