- If you wish to make changes that affect the output of bytecode without having to update the magic number each time (while testing your changes) you can just delete your old .py(c|o) files! Even though you will end up changing the magic number if you change the bytecode, while you are debugging your work you will be changing the bytecode output without constantly bumping up the magic number. This means you end up with stale .pyc files that will not be recreated. Running find . -name '*.py[co]' -exec rm -f {} ';' should delete all .pyc files you have, forcing new ones to be created and thus allow you test out your new bytecode properly.

I propose: 
Any time you make changes that affect the output of bytecode you will need to update the magic number as well, otherwise Python will reuse your old .pyc files and you will not be able to test your new bytecode properly. If you do not wish to constantly bump the magic number you can just delete the old .pyc files each time by running find . -name '*.py[co]' -exec rm -f {} ';'