You can't just change the folder name of a plugin (well you can if you know the rules
). Nor the zipfile name (with the exception of adding a version number). The filename (minus the version suffix) must match the folder name ... which in turn must match the plugin name in the plugin.xml file ... exactly.
The underscore character is reserved for marking where the version suffix of the plugin's zipfile name begins (_vXXX). Everything before that is the plugin name and can't contain an underscore. It throws off the logic of finding the version info.
So yes ... a plugin name can't contain an underscore, but a plugin's zipfile name can (and should). Clear as mud, right?
Also, those looking for a "portable version" of python 3 for Windows should look no further than python.org's newly released Python 3.5. a single line (appdata=local) in a pyvenv.cfg file located in the same directory as the python interpreter renders it an isolated and movable python installation. I haven't checked if they fixed the hardcoded path issue with pip, but I'm betting they have (and there was workaround in place for it anyway). They have an "embeddable" version available for download that already has the pyvenv.cfg file configured (unzip it where you want it and go), but it doesn't include tkinter (yet), so it may not be suitable for all needs. But it's easy enough to "portablize" the full installation by manually creating the pyvenv.cfg file.