Executing the command

SET AUDIT /SERVER=LOCK

locks the security auditing settings, thus preventing any changes.

This is effective until the system is rebooted.

$ sho audit System security alarms currently enabled for:  
ACL  
Authorization  
INSTALL  
SYSGEN  
Breakin:       dialup,local,remote,network,detached,server  
Login:         batch,dialup,local,remote,network,subprocess,detached,server  
Logfailure:    batch,dialup,local,remote,network,subprocess,detached,server  
Logout:        batch,dialup,local,remote,network,subprocess,detached,server  
FILE access:     Failure:     read,write,execute,delete,control
System security audits currently enabled for:  
ACL  
Authorization  
INSTALL  
SYSGEN  
Breakin:       dialup,local,remote,network,detached,server  
Login:         batch,dialup,local,remote,network,subprocess,detached,server  
Logfailure:    batch,dialup,local,remote,network,subprocess,detached,server  
Logout:        batch,dialup,local,remote,network,subprocess,detached,server  
FILE access:     Failure:     read,write,execute,delete,control

$ set audit/server=lock
$ set audit/disable=all/alarm
%SET-E-VERIFYFAIL, specified operation was not performed due to the following error:
-AUDSRV-W-LOCKED, message ignored; audit server locked to prevent change