Say you have two different versions of the same package and want to upload them to
Yes it is possible.
You just upload package twice setting different version (e.g. first
0.1 and second
setup.py of your package.
Here is instruction how to upload: http://peterdowns.com/posts/first-time-with-pypi.html
Then user can install specific version using following command
pip install 'package_name==0.1'
pip install 'package_name<=0.1'