using System;

using System.Linq;

using System.Reflection;

​

var obj = new Foo();

var field = typeof(Foo).GetFields(BindingFlags.NonPublic | BindingFlags.Instance).Where(i => i.Name.StartsWith($"<Hello>")).FirstOrDefault();

field.SetValue(obj, "hello");

Console.WriteLine(obj.Hello);

​

public class Foo

{

    public string Hello { get; } = "test";

}

​