You cannot use another name for SYSTEM but you can add any user to the ADMIN group which gives the user the same privileges as SYSTEM.
The system password can be changed in the server.conf file.
That's why this file must not be readable to anyone else than the system owner (schedulix) and root of course :-).
If you change it there and restart the server the new password will be effective.
.sdmshrc files are user managed files to allow using sdmsh and other command line tools without providing username and password.
It is in the uses responsibility to update those files to reflect password changes.
Think about you have given someone access and he has created a .sdmshrc file for easy login.
You would not be pleased if schedulix would update his .sdmshrc file to match the new password when you intent to changed it was to deny futher access for this user.
You can change the password in the server.conf file and doing 'alter user system ...' to change the password in a running instance.
schedulix will check whether the new password matches the password in server.conf. If not you will get an error message.
This allows to change the system password without restarting the server but keeping it consistent to the server.conf setting.
After changing a password of a schedulix user, all users using this schedulix user to connect have to change their .sdmshrc files and update their connection settings in the web gui (schedulix!Web Users).
If the password change was done by a WebGui manager in the Web GUI, the connection settings of all users using this connection are updated.
If you change a password in the Web GUI to deny users to use the connection any longer, you have to remove the connection by editing the user in the schedulix!Web Users dialog.