modules/project/SPT.SinglePlayer/Patches/MainMenu/EnableRefForPVEPatch.cs

using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using EFT.UI;
using HarmonyLib;
using System.Reflection.Emit;
using SPT.Reflection.Patching;

namespace SPT.SinglePlayer.Patches.MainMenu
{
    /// <summary>
    /// All we want to do with this TranspilePatch is to replace the Ref ID they check for to something different
    /// so this allows the Ref trader to be shown on the TraderScreensGroup
    /// </summary>
    public class EnableRefForPVEPatch : ModulePatch
    {
        protected override MethodBase GetTargetMethod()
        {
            return AccessTools.Method(typeof(TraderScreensGroup), nameof(TraderScreensGroup.method_4));
        }

        [PatchTranspiler]
        public static IEnumerable<CodeInstruction> PatchTranspile(IEnumerable<CodeInstruction> instructions)
        {
            var codes = new List<CodeInstruction>(instructions);
            var searchCode = new CodeInstruction(OpCodes.Ldstr, "6617beeaa9cfa777ca915b7c");
            var searchIndex = -1;
            
            for (var i = 0; i < codes.Count; i++)
            {
                if (codes[i].opcode == searchCode.opcode && codes[i]?.operand == searchCode?.operand)
                {
                    searchIndex = i;
                    break;
                }
            }

            if (searchIndex == -1)
            {
                Logger.LogError($"{nameof(EnableRefForPVEPatch)} failed: Could not find reference code.");
                return instructions;
            }

            // this doesnt have to be anything particular for the string - just cant be a trader ID
            var newCode = new CodeInstruction(OpCodes.Ldstr, "SPT-PVE");

            codes.RemoveAt(searchIndex);
            codes.Insert(searchIndex, newCode);
            
            return codes.AsEnumerable();
        }
    }
}