I finally completed the task today after many tries. I didnt hear a ding either, but once I re-armed my screen froze a second, then the menu popped up. I was able to keep my P40E with 20mms alive for 4 missions, but then had to log.
As I feared there is no way to save the modified plane and I'd have to do it all over again to get the menu up again. Alot of work. But pretty cool.
