Suggestion: remove first parameter, use path for everything

The distinction between "system" and "node" can easily be made without explicitly stating it by looking if the path begins with "node/". This would be easier to users. That would also make the paths match what's in the menu system, allowing you to improve the interface to use Drupal's path registry in the future, e.g. users could search and select paths rather than typing them.

So format would change to a simpler: path|title, e.g. admin/settings/title_override|My New Title! or node/2|ello mate!

And you could add a parameter to title_override_get() to limit results to paths that start with "node/".