This took some time to figure out, after being annoyed by the fact that Android Studio doesn't save the remote URL for a push when you manually enter it.
In the projects .hg directory, create a new file named "hgrc" without an extension. To this file, add the following lines
[paths]
default=url_to/replace_with/your_project
That's it. Should be obvious if you are a Mercurial command line user, which I'm not.
