Along the lines of rewriting bytecode at runtime, https://www.python.org/dev/peps/pep-0302/ lets you arbitrarily hook Python's import process and rewrite .pyc files as desired.

As a practical application, pytest uses this to take the statement `assert foo == bar` and rewrite the AST into a number of instructions that extract the values of foo and bar and print them if the assertion fails: http://pybites.blogspot.com/2011/07/behind-scenes-of-pytests... (https://docs.pytest.org/en/6.2.x/assert.html for those unfamiliar with the library) - so if you use pytest, you're already relying on these arcane techniques!