[DarkFish]

everything's done in the .upc files nowadays
If you open the Data\UPCDataGE\UPCUnitsData\Ammunition.upc file, you will find something like the following in it:

[Ammunition 20]
ID=T3Lut2Torpedo ;Torpedo type
NameDisplayable=T3Lut2Torpedo-Name
Info=T3Lut2Torpedo-Info
Notes=T3Lut2Torpedo-Notes
Type= AmmoTorpedo
Subtype=T_III_LUT_II
AmmunitionIntervalOptionCurrent= NULL, NULL, 0
AmmunitionIntervalOptions1= 1944-02-01, 1944-03-01, 240 ;Date this renown cost starts
AmmunitionIntervalOptions2= 1944-03-01, 1944-04-01, 230 ;Date this renown cost ends
AmmunitionIntervalOptions3= 1944-04-01, 1944-05-01, 220 ;Renown cost anytime between those two dates
.......... ;many many more of these AmmunitionIntervalOptions
AmmunitionIntervalOptions15= 1945-04-01, 1945-09-01, 100
Volume= 1
PackSize=1

If you want the T3Lut2Torpedo to appear in let's say 1940, all you have to do is change the starting date of the first AmmunitionIntervalOption into the desired value.
So:

........
Subtype=T_III_LUT_II
AmmunitionIntervalOptionCurrent= NULL, NULL, 0
AmmunitionIntervalOptions1= 1944-02-01, 1944-03-01, 240 ;February 1st, 1944
AmmunitionIntervalOptions2= 1944-03-01, 1944-04-01, 230
........

becomes:

........
Subtype=T_III_LUT_II
AmmunitionIntervalOptionCurrent= NULL, NULL, 0
AmmunitionIntervalOptions1= 1940-01-01, 1944-03-01, 240 ;January 1st, 1940
AmmunitionIntervalOptions2= 1944-03-01, 1944-04-01, 230
........

hope this helps