This is new functionality included in R8 but for R7 you can create a custom scripting component that mimics the text tag and exposes the Font set method:
https://developer.rhino3d.com/api/rhinocommon/rhino.geometry.annotationbase/font
You may be able to set the “default” font by modifying some document properties or perhaps setting it inside an .ini file or something in the install directory but I haven’t tested that idea.
The code from this post could be modified to change the font as well:
Otherwise, you have this plugin available to you which will do what you want:
I think Elefront can also do this in R7 but It’s been a minute since I’ve used it so I don’t recall.
I hope some of this helps you!