I think I figured it out
In order to do the changes in the torpedo.sim file automatically, one has to add the following lines to Randomised events.cfg:
;----------Adapt initial depth in data\Library\Torpedo.sim for TI,TII,TIII begin----
[0:data\Library\Torpedo.sim]
ApplyToPeriod=19390101|19420531
;Or 19390101|19450508 for whole war
;No randomization
ChooseFrom=1
RndMidPat=1
0_x0CCF=2 ; initial depth for TI
0_x0E7B=2 ; initial depth for TII
0_x0FE7=2 ; initial depth for TIII
;----------Adapt launch depth in data\Library\Torpedo.sim for TI,TII,TIII end----
I would be very happy if someone who knows more about these values than I do could confirm them. It seems they are correct for stock SH3, GWX and NYGM (at least an older version. I don't know whether the file has been changed since then). So, if one uses a modified Torpedo.sim file then it is good to check these values again.
Cheers, LGN1