Ok I understand which part are you taking about, ordnance Template from the ship screen.
However my waship is designed as collier and it has a magazine system, but from the menu' where you can set which missles to load, I can actually see my only design, not the one from the precursor.
Hannover class Missile Cruiser 12.660 tons 372 Crew 1.873.5 BP TCS 253 TH 300 EM 0
2369 km/s Armour 4-48 Shields 0-0 HTK 76 Sensors 50/50/0/0 DCR 12 PPV 40
Maint Life 4.89 Years MSP 1.109 AFR 107% IFR 1.5% 1YR 77 5YR 1.152 Max Repair 420 MSP
Magazine 100
Fregattankapitan Control Rating 1 BRG
Intended Deployment Time: 24 months Morale Check Required
Nuclear Pulse Engine EP200.00 (3) Power 600 Fuel Use 354.18% Signature 100.0 Explosion 20%
Fuel Capacity 3.000.000 Litres Range 12 billion km (58 days at full power)
Wurm-Neubauer Size 10 Missile Launcher (4) Missile Size: 10 Rate of Fire 95
Wertmüller Electronic Systems Missile Fire Control FC135-R100 (50%) (1) Range 135.8m km Resolution 100
Nagel Precision Arms Admiralty Islands Anti-Ship Missile (25) Speed: 11.200 km/s End: 105m Range: 70.6m km WH: 2 Size: 4 TH: 37/22/11
Ordnance Transfer Rate: 40 MSP per hour Complete Transfer 2.5 hours
Roentgen & Seydlitz Active Search Sensor AS135-R100 (50%) (1) GPS 33600 Range 135.8m km Resolution 100
Ackerman Electronics EM Sensor EM10-50 (1) Sensitivity 50 Detect Sig Strength 1000: 55.9m km
Ackerman Electronics Thermal Sensor TH10-50 (1) Sensitivity 50 Detect Sig Strength 1000: 55.9m km
ECCM-1 (1) Missile to hit chances are vs targets moving at 3000 km/s, 5000 km/s and 10,000 km/s
This design is classed as a Military Vessel for maintenance purposes
Also, I tried to change the missles from the ship design window, but I can only choose my designed missles only.
The only reason I can think is that those precursors missles are bigger then my Launchers, but I cannot see the specifics anywhere.