Change Keynote Default Fonts, Layouts

How do I change the default fonts and layout style in Keynote.app? This is Keynote downloaded from the App Store.

For example, I'm beginning with the basic "White" theme, which uses Gill Sans as the default font. I need Optima. (And so on.)

I discovered, consistent with this archived thread, that I can edit all the master slides by hand, but this still doesn't change the default font: whenever I add new text, either to the master or to the presentation, it's always Gill Sans. I want Optima to be the default font, so that when I add new text, it's always Optima.

I also looked in the Keynote.app file

$ sudo vi /Applications/Keynote.app/Contents/Resources/Themes/White_1280x720.kth/Contents /Resources/en.lproj/fontsAndText.strings

and see this:

"STYLE_Series_2" = "Series_2";

"STYLE_None" = "None";

"STYLE_Series_5" = "Series_5";

"STYLE_Series_3" = "Series_3";

"FONT_LucidaGrande" = "LucidaGrande";

"FONT_Helvetica" = "Helvetica";

"STYLE_Free Form" = "Free Form";

"STYLE_Series_1" = "Series_1";

"FONT_GillSans" = "GillSans";

"STYLE_Normal" = "Normal";

"STYLE_Series_0" = "Series_0";

"FONT_MarkerFelt-Thin" = "MarkerFelt-Thin";

"STYLE_Series_4" = "Series_4";

But I don't see how to edit this to make Optima the default font in my theme. I also edited my .key file and greped for GillSans and Optima, and don't see either string in my Keynote presentation.

How do you specify the default font in Keynote? Is this possible? What about other defaults, like line widths, colors, styles, and so forth.