Is it possible to attach a HD, erase it, remove it, add content to the hd and replace it to the Tablo with the goal of streaming the content on the local network
Not with the Tablo.
It sounds like you want something more like a Plex or a Jellyfin media server.
Tablo will only work with it’s own recorded content, which itself is not easy to extract on the Gen4. There is software for the Legacy to do that.
Not with the tablo. But if you are using a Roku there is a media player app for the Roku, so you can use the Roku to play content stored on that drive.
To clarify @robert2’s comment, you shouldn’t use the active Tablo HD for this. You would need a separate HD that already has content on it. Here’s an article from Roku. I’m sure there are similar articles for FireTV and AppleTV. Many TVs natively support DLNA too.
Sorry - That is absolutely correct. You can attach a SSD or hard-disk directly to your Roku, and use the Roku media player to play your recordings from the device attached to the Roku.
Only the Tablo can play recordings on a drive attached to the Tablo, and then only if they are recordings make by the Tablo.
Sorry for being imprecise.