There are specific parameters that you can override on your //EXEC PARM= card for the XCOM STC. Here is the list of the valid parameters.
Release: XCOM for z/OS
The following processing options can be overridden by the PARM parameter:
ACBNAME EDESC LOGMODE START AGE EROUT NETNAME SWAIT ALLOC ERRINTV PRI TCPSTACK CATALOG FERL PSOUNIT TERL CLASS IDESC PSOVOL UNIT COMPNEG IROUT REMAGE USERD DFLTVER JESINTV SEC VTAMGNAM DFLTAB LOG SERL VERL DIR LOGCLASS SMF VOL DOMAIN LOGDEST SMFNUM XCOMPLEX DUMPCL
If the parameter is not part of the above list you will then be required to modify the value of that parameter within your config member. For the changes to take effect you would have to recycle your XCOM STC. Please refer to Configure the default options.