Is there a way to change the theme but allow updates?

I modified the theme to disable the printing of the text “Category Archive: %s” in one of the theme .php pages (can’t remember which one). My concern is that when I go ahead and continue to tweak this theme, any update will erase all these changes. Is there a way to fork the theme edits but still allow updates to the theme to occur in some elegant way? Or do I just have to keep track of my changes elsewhere and reapply them later?