Well, on a different note, if you have a scripted language application, you typically can edit files and bypass whatever you want on the application. In fact, I'd bet most modern software isn't signed; and even if it is, sometimes the libraries that get compiled in into that signed binary... aren't.

I can change the behaviour of many/most applications by just having read/write access to files; Can you give me examples of mainstream applications that are resistant to filesystem tampering when eg.you have install access? Maybe I'm missing something.