WordPad Workaround
The problem is that WordPad doesn't let you choose a default font, it's always Calibri 11, line spacing 1.15, and 10pt spacing after paragraphs. You can't change WordPad, but you can easily open new .rtf documents with default settings of your choice.
Create an .rtf template file
(Note: For now, this is called "template.rtf", but you can name it anything you want.)1. Open a WordPad document. Type a space with the space bar. Click Ctrl+A to select the space.
(Note: If there is no "space" to select, your changes will not persist.)
2. Make your changes to font, size, line spacing, etc.
3. Click on the WordPad dropdown (top left corner).
4. Select "Save as" > "Rich Text Document" to your Desktop, naming it...