Editing DefaultFonts.plist
doesn't seem working anymore on the pre-release build 15A279b of El Capitan:
sudo vim /Applications/Notes.app/Contents/Resources/en.lproj/DefaultFonts.plist
It still shows that the file is readonly. I guess it's because the new System Integrity Protection feature.
Is there another way to change the default font in Notes app?
defaults read com.apple.Notes NoteFont
(?)