It would actually apply to each submarine's UPCGE (plain UPC for Allied subs) file, found in "Data / Submarine / SubName / Subname.upc". If you have a Type VIIC, you'll find in the "NSS_Uboat7c" folder, "NSS_Uboat7c.upcge" files lines like:
MaxPettyOfficers=15 ; max number of crewmembers over rank 4
MaxOfficers=8 ; max number of crewmembers over rank 7
Change those figures to like 30 and 16 or whatever. Not "historic", but neither are the original figures...