Once you’ve made and applied this change it will not be possible to connect to ssh as root. You have a couple options to use instead:
Log in via SSH with the new user account you created in that tutorial and use
sudo to run commands as root or
sudo su to launch a shell as root after you are logged in.
If for any reason you are not able to log in with the new account, if you are using password authentication (instead of ssh-keys) you can log into the web console in the control panel (Droplet->Access->Console) as root. The console is not powered by SSH. Instead, your droplet sees the console as it’s local keyboard and display.