In the past, with 0.7.x, I could replace some calibre sources in a binary install on windows. The files reside under Lib/site-packages/calibre/ .
After upgrading to 0.8.17 I notice this folder is no longer there.

What is the current method to replace just a few of the Calibre source files in a binary install?

Run calibre from source, see http://manual.calibre-ebook.com/develop.html#windows-development-environment

So the alternative you suggested last year doesn't work anymore?

kovid@> search for the filename of the file you want to replace without the .py extension
kovid@> look in lib/site-packages/calibre

All the python files are now inside pylib.zip, you could replace them in there if you really wanted to, but running from source is a lot easier.

In this particular case for this particular end user, replacing the files in pylib.zip is more practical, and works like a charm. Thanks for the suggestion.