Changing a cfg file for mission aircraft of choice??

Hey everyone, does anyone know how, or if its possible to change what aircraft is used for a default mission? The africa relief mission for instance, if I wanted to change the aircraft to be a helicopter instead of the DC3, how would I go about this? The problem I have now is, if I have changes allowed checked before I start the mission, the helicopter keeps trying to start over and over and never starts no matter what, even if I shut everything off first on the DC3 before changing aircraft. I thought now, the best way when I load the mission, it already loads the heli of my choice from the beginning and hopefully I don't have this issue. Thanks for your help. :)