Permanently change the default font in Writer 5
Create a template where the font you want to be your default is assigned to the ‘Default Style’ paragraph style and make this template your standard.
If you don’t wanna make default templates for everything just to change the font, LO has integrated global font replacement settings where you choose the original font and what font you replace it with, and where it gets used. Since it’s global it affects every program under LO as dictated by the “rules” of usage.