create custom font? click to apply changes?

I'm having to change text boxes one-by-one on a large Keynote file. Is there a way to save my own custom font (Helvetica 24, Left-justifc), then highlight each text box and apply my custom font?

I'm working on a very large file, and I'm having to make these changes one at a time, which is taking forever. The "select all" function won't allow me to make changes.