What commands are available to pass ass commands when starting up an AX client?
You can find all of them in the SysStartupCmd class in the construct method.
If you want to add your own command you can create a new class which extends the SysStartupCmd class and add it as a new case in the construct method.
For other client commands see https://technet.microsoft.com/en-us/library/aa569653.aspx. For example you can find out how to bypass changes made to startup of AX for clients.