Re: Windows Store
The default sub-system (Ubuntu) is installed via the Add/Remove Features settings page, so you don't need to touch the store and give MS an email address.
How much work it would be to manually swap out the version of Ubuntu and replace it with something else I don't know, but the linux filesystem can be found at
%localappdata%\lxss, so I suspect it's possible, if tricky.
Oops, I spoke too soon, someone has already written scripts in python to download and install new distros.