Jonathon is correct, in that double clicking gets you to The small dialog box shown. Choose Title Block Layout, which brings you to a completely editable Title block wher you can edit any text as you see fit.
I think I'd then save the edited Titleblock as a new style.
Note that I do not think this edit changes text over in the last dialog box shown, which is the Titleblock Manager
that window any text which is in Italics is editable, that which is non-italic is NOT editable. Text edited on right side of colon becomes default text I believe.