Trying to stop a domain being abused

CallingClass.cs

using System;
using ImmutableDomain.Commands;
using ImmutableDomain.Entities;
using ImmutableDomain.Help;

namespace ImmutableDomain.Other
{
    public class CallingClass
    {
        private readonly IRepository repository;

        public CallingClass(IRepository repository)
        {
            this.repository = repository;
        }

        public void DoSomething()
        {
            var command = new CreateEmployeeCommand(new Guid(), "Jim", "Smith");

            // command.FirstName = ""; YAY we can't mess with it. 

            // we can't create this in the wrong assembly
            // var employee = new Employee(new Guid(), "", "");

            var employee = this.repository.Get<Employee>(Guid.Parse("F3E11CF0-89E6-44AD-B557-B32A0832D6E1"));

            // we can't overwrite the name
            // employee.FirstName = "";

            // we need to use the IEditableEmployee to update the employee
            // but it's internal so it must be used in the right assembly
            //(employee as IEditableEmployee).Update("Jim", "Hoff");


        }
    }
}