Copy that title block into a new blank drawing based on your current template, then save it again as a template over your existing one. This sets it for all your future new drawings.
For the existing drawings, once you open it up and find that you've got an out of date title block, just open up a new blank drawing - since you've already saved the new block to your template - and then copy-paste either just the new title block itself over to the old drawing, or you can bring the whole Drawing Resources folder over. This will bring sketch symbols, borders, etc., as well. I wind up doing this a lot - over the last 10 months or so I've been constantly adding new little automations and sketched symbols to my template, as well as title block changes, so I just bring the whole thing over in one shot.