ClientMods/MagazineInspector/Plugin.cs

using Aki.Reflection.Patching;
using BepInEx;
using System.Reflection;

namespace IcyClawz.MagazineInspector
{
    [BepInPlugin("com.IcyClawz.MagazineInspector", "IcyClawz.MagazineInspector", "1.2.0")]
    public class Plugin : BaseUnityPlugin
    {
        private void Awake()
        {
            new MagazinePatch().Enable();
        }
    }

    internal class MagazinePatch : ModulePatch
    {
        protected override MethodBase GetTargetMethod() =>
            typeof(MagazineClass).GetConstructors()[0];
        
        [PatchPostfix]
        private static void PatchPostfix(ref MagazineClass __instance)
        {
            __instance.AddAmmoCountAttribute();
        }
    }
}