sample.cs

using System.Linq.Expressions;
using System.Reflection;
using System;

static class P
{
    class Foo
    {
        public Guid Value => _value;
        private readonly Guid _value;
        public Foo(Guid value) => _value = value;
    }
    static void Main()
    {

        var clone = Expression.Parameter(typeof(Foo), "clone");
        var value = Expression.Parameter(typeof(Guid), "value");
        var fieldInfo = typeof(Foo).GetField("_value", BindingFlags.NonPublic | BindingFlags.Instance);

        // ** what we broadly want - but the Expression API disallows because of init-only
        // "Expression must be writeable (Parameter 'left')"
        // var body = Expression.Assign(Expression.Field(clone, fieldInfo), value);

        // long-winded and inefficient way of doing the same thing
        var expression = Expression.Convert(value, typeof(object));
        var body = Expression.Call(Expression.Constant(fieldInfo), fieldSetValue, clone, expression);

        var action = Expression.Lambda<Action<Foo, Guid>>(body, clone, value).Compile();

        var obj = new Foo(Guid.NewGuid());
        var newGuid = Guid.NewGuid();
        Console.WriteLine($"original: {obj.Value}; pushing {newGuid}");
        action(obj, newGuid);
        Console.WriteLine($"final: {obj.Value}");
    }
    static readonly MethodInfo fieldSetValue = typeof(FieldInfo).GetMethod(nameof(FieldInfo.SetValue), new[] { typeof(object), typeof(object) });
}

Hi,
The above code is similar except for line #18, where my code is slightly different which is as below:
var fieldInfo = typeof(Guid).GetFields(BindingFlags.NonPublic | BindingFlags.Instance);

I am not sure of the purpose to use an array of fieldinfo. This array returns the value in Int32, Int16 & byte[] format & this fails in Expression.Call.

This is where I need help.

@neerajsahani-logianalytics "I am not sure of the purpose to use an array of fieldinfo." - well, that's your code, not mine - I don't use an array; I can't say anything about your code without being able to see your code