PrePlugin.cs

using Microsoft.Xrm.Sdk;
using System;

namespace Plugin
{
    public class TestPlugin : IPlugin
    {
        public void Execute(IServiceProvider serviceProvider)
        {
            var tracing = (ITracingService)serviceProvider.GetService(typeof(ITracingService));
            var context = (IPluginExecutionContext)serviceProvider.GetService(typeof(IPluginExecutionContext));
            var factory = (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));
            var service = factory.CreateOrganizationService(context.UserId);
            Entity entity = new Entity();
            Entity preImage, postImage;

            if (context.InputParameters.Contains("Target") && context.InputParameters["Target"] is Entity)
                entity = (Entity)context.InputParameters["Target"];
            if (context.PreEntityImages.Contains("PreImage") && context.PreEntityImages["PreImage"] is Entity)
                preImage = context.PreEntityImages["PreImage"];
            if (context.PreEntityImages.Contains("PostImage") && context.PreEntityImages["PostImage"] is Entity)
                postImage = context.PreEntityImages["PostImage"];

            entity["jobtitle"] = "Working";
        }
    }
}