Create a title and change the font and anything else that you want.
At the top of the Text Editor window, open the dropdown, Save as Title Template. Give it a name and save it, first noting the path to where it will be stored.
Go to the path in Windows Explorer and change the existing title "title.tfx" to "arial.tfx" or something else. I don't suggest deleting it. Rename your new template to "title.tfx". Open a new project. Add an image, add a title. The new title should be with the new default font (with anything else that you wanted).
Note that in my image above, I had a font size of 55 when I saved the template, thus whenever I use this, it will be the new font and size.