I have updated our company drawing title blocks also. I am usually in the drawing and editing when I realize that the the title block needs to be updated. In this case, what I do is start a new drawing (will have the updated template), then open up Drawing Resources>Title Blocks (at the top of the drawing browser), select and copy the latest title block(s), go to the drawing needing the update, click on the "Drawing Resources" folder and paste (the title blocks will be placed in the proper sub-folder). If your new title block has the same name as the old one, it will ask if you want to replace ... say yes. If the names are different, it is your option to delete the old title block definitions.
Not as elegant as @CCarreiras solution but it works while you have the drawing open.
Inventor Pro / Vault Basic