You mean "Esc" while the 1st screen is bouncing ?
I would like you explain me clearly the goal of the exit number, i can be interesting.
I don't know if it is possible to do (I have checked a little in the documentation). but if it's not possible to do maybe I can made it exit with an error so you can check this number ??
another solution is to add ASM code that allow to do that.
My next objective is maybe to add a configuration screen because for people not familiar with the Amiga, maybe it's awkward to modify the startup-sequence to configure the program.