the sheet format, and everything else in the template is copied into the new drawing when created. these are NOT linked (thank goodness).
You could link the tolerances to a custom property and then use Custom Property Tab Builder to update the drawings that need the new tolerances. But I agree with Jeremy Feist having it update system wide could be a very expensive prospect.
I agree it's not linked, unless you want it to be. I suggest it not.
To change it means the tolerance changes for that part, making a revision change.