It's cleaner to add the repository as a separate file. So instead of

• echo "deb http://www.linuxmint.com/repository romeo/" >>/etc/apt/sources.list

You could use something like

• echo "deb http://www.linuxmint.com/repository romeo/" >>/etc/apt/sources.list.d/romeo.list

You could also use wget to download a premade romeo.list file to the appropriate location.

You could also pipe the output of the echo command into the tee command to create the list file. For example:

•  echo "deb http://www.linuxmint.com/repository romeo/" | sudo tee /etc/apt/sources.list