There is no IEASYSxx parameter to set MSGFLD=xx, but the MSGFLDxx suffix can be specified in CONSOLxx. It can also be set at any time using the SET MSGFLD= command.
When MSTRJCL=(xx[,L]) is specified on IEASYSxx, JCL messages issued for master scheduler processing are routed to consoles that receive operator information (routing code 2) or system/error maintenance (routing code 10) messages. Use MSTRJCL=(xx[,L]) only for debugging purposes. See IEASYSxx (system parameter list).