There are always corner cases where you might need to do something differently. I had three memorable cases in my career: 1. Python 2.6x had a a stdlib bug where windows event logging did crash the process when the user had some rights set differently. Fix submitted but for the meantime we simply overwrote the private function and could ship. 2. Also python: scikit-learn had a primitive "print everything" strategy, but we need to get it into a logging framework. We overwrote their print wrapper and could ship. 3. In C#, a third party lib insisted on dumping a result to a file. We used reflection to get that as a stream.

All three are not ideal - but I think having escape hatches is important. I also think private/public is overrated. Having it as a signal is ok. Forbidding access to privates is too strong.