You can add SSH keys to DigitalOcean which can then be selected during the droplet create process to add the selected SSH keys under the root user.
When using SSH keys a root password will no longer be set as SSH keys will be used as the preferred method of access.
We do not manage the server after creation, so editing, adding, or removing SSH keys from the SSH interface will not affect any of the stored keys on droplets that you have created.