I tried the following:

strtofile(chr(27)+'%-12345X@PJL RDYMSG DISPLAY="MESSAGE HERE"',"hpDisplay.txt")
!copy /b hpDisplay.txt \\server\printer

and also tried with doing a net use lpt1 \\server\printer and then

!copy /b hpDisplay.txt lpt1

Neither one got the display on the printer to change.
Anyone know what I am doing wrong?