Hi CS
I asked a question here:
http://forums.ubi.com/groupee/forums/a/tpc/f/23110283/m/9751098443
What I was trying to do was load a Pearl Harbour attack mission..and change the skins for all the aircraft. I could do do for Vals, Zeros and the P-40s. However, I also wanted to add some nicer skins for the Kates (which are not player flyable) but the option was blanked out. The mission wasn't created with Mission Mate perhaps that is the reason?