The problem I had had nothing to do with the 1939 XXI mod. It was related to a patrol ending in one year and starting the next one in another, apparently:

http://www.subsim.com/radioroom/show...=143816&page=8

Jeez I hate it when something so coincidental happens like this :damn:

My apologies to the modders...I just went ahead and ran the January 1941 patrol with the unchangeable loadout, and my next patrols have worked fine (I can change loadouts and it "sticks").

Sheesh!