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";
}