You can just fork the library and point your requirements.txt to e.g. git+https://github.com/yourusername/librarything.git@yourbranch for the time being.
(Via my comment.)
So here's my situation:
I am working on chess software and to make it work I had to change one line of MIT-licensed library which I am using in my project. Modified library is in my virtual environment which is not included in my GitHub repository because I've read that is a bad practice to include venv into GitHub repo. Someday I'd like to share with my project to the chess world and I don't know how to handle this modified library. Normally without any changes I'd just include requirements.txt so a user could simply install it with pip. But here I can't do that because it'd download a library without necessary change. I have some ideas how to handle that but none of them seems optimal. Thanks in advance for any help!
PS. I know it's not strictly programming related question but honestly I don't know a better place to ask it.
How to properly share modified MIT library on GitHub?