Beats me, I add resupply bases and use Mark 14s, I found with the 16s it was TOO easy, no challenge when you can knock them off 4 miles away.
Adding more tubes is relatively simple;
http://www.subsim.com/radioroom/show....php?p=2600351
I didn't look into adding more reloads, limit is probably how much space is in the reload screen.
Twin mount 40s I found crashed the game if they were added forward;
http://www.subsim.com/radioroom/showthread.php?t=240965
Although they work fine on the aft AA platform. A twin 40 aft and a single 40 forward causes no problems, don't know why.