If you start your tests from an existing project where you have all your scripts configured then you can't set SLA metrics as command line option to override or add new ones.

However if your scripts are not too complex you could run your test as code based on a yaml file. By doing this you can setup in your yaml file your SLA's. Still you can't pass the SLA's as command option but it's much easier to modify your yaml file to suit your needs based on the test you would like to launch.

For more information about NeoLoad as code you can check the documentation here