apt-src

manage Debian source packages
apt-src is a command line interface for downloading, installing, upgrading,
and tracking Debian source packages. It makes source package management
feel a lot like using apt to manage binary packages, and is being used as
a testbed to work on adding source dependencies to Debian.
.
It can be run as a normal user, or as root. If you want a convenient way to
track updates to packages while preserving your local modifications, this is
a way to do that.