I don’t believe you can change quite everything with the equation editor, but I have not tried installing something like “math type,” which some people like.
You can, however, click inside your formatting options (within the standard equation editor) and convert highlighted equations to “normal text” and then choose a font, but it will only usually change the letters and numbers, and sometimes messes up exponent sizes, depending on the font. It will not change your radical bars, division bars, etc.
If anyone else has found a good way, please jump in! 🙂