I understood that this could've been done before using the NPAPI, but since it's gone is there like .. any other way to access the Windows' registry using a Chrome extension ?
The answer should be no, since extension lives in the sandbox and you can only do that using plugin with NPAPI, which has been permanately removed in the latest chrome.
The answer could also be yes, you can use Native Messaging to exchange messages between extensions and native applications, then you can access the registry in the native app.