Programming considerations:

This exit is taken only for $WTOs issued from the JES2 main task.
To cancel a message, pass a return code of 8 to JES2. This return code directs JES2 to bypass the HASPWQUE routine, which normally queues the CMB for the console service processor, and to give control directly to the $FRECMBR routine, which then discards the message by freeing its CMB.
To change the text of a message, your routine must access either the CMBTEXT field or the CMBJOBN field. If the message does not contain the job's name and number, the message text starts in CMBJOBN. The length of the message is always in the CMBML field. Your routine can either retrieve the existing message text and modify it or else generate a completely new message and then write the new or modified message over the original message. If the new or modified message is longer or shorter than the original message, your routine should alter the CMBML field accordingly. After altering the text of the message, pass a return code of 0 or 4 to direct JES2 to queue the CMB for transmission. JES2 will then send the new or modified message.
CAUTION:
Altering or deleting an end-line of a multi-line WTO can put JES2 command processing in a Wait State and no more responses to commands will be received.
To alter a message's console routing, your routine should first test the flag byte CMBFLAG to determine whether the CMBFLAGW, CMBFLAGT, and CMBFLAGU flags are off. If these three flags are off, the CMBROUT field contains the MVS™ console routings. After altering CMBROUT, pass a return code of 0 or 4 to direct JES2 to queue the CMB for transmission. JES2 will base its console routing on the new contents of CMBROUT.
If register 0 contains a value of 4 when this exit is invoked, do not take any action that will result in a wait. For example, do not issue a $WAIT or do not invoke another service, such as $QSUSE, that might issue a $WAIT. A $WAIT can cause problems such as line time-outs or cause JES2 to terminate.