Your Tablo TV Guide Service subscription is tied to YOU, not a specific device.
You can change or upgrade to a new Tablo DVR and keep your existing TV Guide subscription.
Unless you’ve had your Lifetime Subscription in place prior to 3/07/2019 - A Message from the CEO Re: Subscription Account Changes
As for the drive, this step by step guide works well for most (I’ve used it issue free)
The DB …recording schedule “stuff”, guide data, channel info, etc is stored internally. So without the drive the “old tablo” will still have every thing there. Well, it will show recordings, but you know they aren’t. As I understand, overnight maintenance mode
Should clean up all the orphan recordings.
You “new tablo” will have everything your “old tablo” had - including it’s Name from the settings tab. May want/to change that since now you’ll be selecting which device to use. (the apps know the difference… but will you)
So yes you can “swap drives” (although that’s not what it’s called!). It’s unlikely you can add your new tablo to your subscription, but there’s a possibility.