Need to create file in /System/Library/LaunchDaemons/

I have a script to manage and make TimeMachine speed mode setting persistent at next boot by using /System/Library/LaunchDaemons/nothrottle.plist file.

When it is not being used, script needs to create it but it's failing since Catalina and was working until latest fixes in Mojave.

Sample error messages:

sudo launchctl unload -Fw /System/Library/LaunchDaemons/nothrottle.plist
/System/Library/LaunchDaemons/nothrottle.plist: No such file or directory


echo "<TEXT>" >>/System/Library/LaunchDaemons/nothrottle.plist
/System/Library/LaunchDaemons/nothrottle.plist: Operation not permitted


Does any1 have a clue about it ?
Need to create file in /System/Library/LaunchDaemons/
 
 
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