I tested the ResetHandler program from http://http://aminet.net/package/util/boot/ResetHandler with the 2012-04-18 AROS boot ROM. The archive includes source code.
The program should print banner text to the CLI, then install a keyboard.device reset handler (which shows a window with ten-second countdown message when the user presses Ctrl-Amiga-Amiga). I don't know whether AROS keyboard.device supports reset handler commands, but that's probably not relevant here.
When run under the AROS ROM, it just exits silently.