minecraft-kajetans-core-mod/src/main/resources/class_transformer/playerlist.js

var transformerName = "Dedicated Server Transformer";
var ASMAPI = Java.type('net.minecraftforge.coremod.api.ASMAPI');
var Opcodes = Java.type('org.objectweb.asm.Opcodes');
var VarInsnNode = Java.type("org.objectweb.asm.tree.VarInsnNode");
var MethodInsnNode = Java.type("org.objectweb.asm.tree.MethodInsnNode");
var LineNumberNode = Java.type("org.objectweb.asm.tree.LineNumberNode");

function initializeCoreMod() {
    return {
        transformerName: {
            'target': {
                'type': 'CLASS',
                'name': 'net.minecraft.server.dedicated.DedicatedServer'
            },
            'transformer': function (classNode) {
                var methods = classNode.methods;

                var targetMethodName = ASMAPI.mapMethod("func_71197_b"); // init
                var targetMethodDesc = "()Z";

                for (var i in methods) {
                    var method = methods[i];
                    if (method.name.equals(targetMethodName) && method.desc.equals(targetMethodDesc)) {
                        transform(method);
                        break;
                    }
                }
                return classNode;
            }
        }
    };
}

function transform(method) {
    var instrList = method.instructions;
    for (var i = 0; i < instrList.size(); ++i) {
        var instr = instrList.get(i);
        if (instr.getOpcode() == 183 && instr instanceof MethodInsnNode && instr.owner == "net/minecraft/server/dedicated/DedicatedPlayerList") {
            instrList.remove(instrList.get(i));
            instrList.remove(instrList.get(i));
            instrList.insert(instrList.get(i), new MethodInsnNode(Opcodes.INVOKESTATIC, "me/kcm/Hooks",
                    "setPlayerList",
                    "(Lnet/minecraft/server/dedicated/DedicatedServer;Lnet/minecraft/util/registry/DynamicRegistries$Impl;Lnet/minecraft/world/storage/PlayerData;)V",
                    false));
            break;
        }
    }
}