I’m afraid that you can’t do what you want to do within SEU itself.
The ideal place to send your message would be the message subfile at the bottom of the SEU display, unfortunately you can’t send a message there until SEU is in the call stack.
It may be possible, I haven’t tried, to use the QIBM_QSU_LCMD exit point for the SEU User Defined Line Commands and write a program that sends a message to the program message queue from there. Scan Google (or the archives) for references to the exit point.
When SEU is loaded there is a copyright message showing at the bottom of the display. If you can find where the message is held you could always change that to the details of your own message (although the copyright text could be generic and used by other applications).
Depending on exactly what you want to achieve by displaying a message to the user, does the message have to be on the SEU screen? If it is simply a policy type warning message along the lines of “Only authorised programmers are aloud to use SEU” then I would suggest putting the call to SEU inside your own wrapper program and using either SNDPGMMSG MSG(‘text’) TOPGMQ(*EXT) before the call to SEU or design a screen display and allow the user the chance to back out from loading SEU.
Hopefully the above ideas will give you something to think about.