To change ammo:
1. locate the Basic file under this path: Silent Hunter 3/data/Cfg/Basic
2. backup this file
3. locate the MaxAmmoPerSlot and
4. locate the ammo types as follows: [ammo_type0];10.5cm SK C/32 and [ammo_type1];8.8cm SK C/35 and change the number of shell you desire.
5. save file
These are my changes to the Basic file, I went to all HE shells, for example:
close to the end of the file & located just below [TORPEDO_TYPE9];
[SUBMARINE_AMMOLIMITS1] ;105mm
MaxAmmoPerSlot=250
[SUBMARINE_AMMOLIMITS2] ;88mm
MaxAmmoPerSlot=250
then, located just below [CONING_TYPE12] ;XXI/1
[AMMO_TYPE0];10.5cm SK C/32
Idx=0
Year=1939
Month=1
AP=0
HE=250
SS=0
Renown=0
[AMMO_TYPE1];8.8cm SK C/35
Idx=1
Year=1939
Month=1
AP=0
HE=250
SS=0
Renown=0
---------------------------------------------------------------------
This is a little tedious but to change weather conditions to use deck gun and flak guns in stormy weather:
1. locate
all submarine files under this path: Silent Hunter 3/data/submarine/NSS_Uboat***/NSS_Uboat***
2. backup these files
3. in each and every sub file, look for [Properties] and increase StormConditions= to 10 or 11 (I use 11 for example as follows

4. save file
StormConditions=11,1;max wind speed [m/s], max rain intensity [0,1]
This change must be made in each & every submarine file.
Hope this is helpful.