SampleBehaviour.cs

using System.Collections;
using System.Collections.Generic;
using Unity.IL2CPP.CompilerServices;
using UnityEngine;

[Il2CppSetOption(Option.NullChecks, false)]
public sealed class SampleBehaviour : MonoBehaviour {

    struct Point
    {
        public int x;
        public int y;
    }

    Point[] points = new Point[]
    {
        new Point(){y = 1},
        new Point(){y = 2},
        new Point(){y = 3},
    };

    [Il2CppSetOption(Option.ArrayBoundsChecks, false)]
    void Awake()
    {
        int length = points.Length;
        for (int i=0; i< length; i++)
        {
            var p = points[i];
            p.x = p.y;
            points[i] = p;
        }

        var p2 = points[2];
        p2.x = 12;
        points[2] = p2;
    }

    void Start()
    {
        for (int i = 0; i < points.Length; i++)
            Debug.Log(points[i].x);
    }
}