make custom user agent change permanent

launchd plist safari user-account

You can set it with defaults write:

defaults write com.apple.Safari CustomUserAgent "\"useragentstring\""

Related

Spotlight: Don't Index a Volume
Permissions of /Users keep changing back to drwxrwxrwx
Is there a way to tweet from a keyboard command?
Bluetooth Not Available?
How to transfer Clash of Clans from one iOS device to another
How to correctly use the extern keyword in C
How do I use namespaces with TypeScript external modules?
MVC for advanced PHP developers [closed]
How do I adjust the anchor point of a CALayer, when Auto Layout is being used?
How to remove convexity defects in a Sudoku square?
How does Content Security Policy (CSP) work?
Understanding NumPy's einsum