How to modify the launchctl config to start Postfix?

On Sequoia, I want to configure my postfix as a server. And for this I have to change the way postfix is started from:

/System/Library/LaunchDaemons/com.apple.postfix.master.plist

But this file is on the read only / file system.

Then I just unloaded this startup, and made a new one in:

/Library/LaunchDaemons/com.apple.postfix.master.plist

and I was able to start it.

But on the next system boot, the system one in

/System/Library/LaunchDaemons

was started again.

How should I cleanly and permanently achieve this server basic modification?

How to modify the launchctl config to start Postfix?
 
 
Q