Programmatically changing the "message" for the express VI prompt user for input

[Robert Stephen]

I was setting up the express vi "prompt user for input" and wandered
if it was possible to programmatically change the message like the
"Display Message to User".
I tried converting to a sub_vi and adding a control, wiring it to the
indicator, hiding the control and adding the input to the connector
but it doesn't seem to do anything.
Any suggestions?