ReadonlyBlocks.cs

using System;
using System.Collections.Generic;
using EPiServer.Core;
using EPiServer.Framework;
using EPiServer.Framework.Initialization;
using EPiServer.Shell.ObjectEditing;

namespace Foundation.Features
{
    public class ReadonlyBlockMetadataExtender : IMetadataExtender
    {
        public void ModifyMetadata(ExtendedMetadata metadata, IEnumerable<Attribute> attributes)
        {
            // Check it's a block
            if (metadata.Model is BlockData)
            {
                // Logic to decide if the user should be able to edit or not lives here
                foreach (var modelMetadata in metadata.Properties)
                {
                    var property = (ExtendedMetadata)modelMetadata;
                    property.IsReadOnly = true;
                }
            }
        }
    }

    [InitializableModule]
    [ModuleDependency(typeof(EPiServer.Cms.Shell.InitializableModule))]
    public class SiteMetadataExtenderInitialization : IInitializableModule
    {
        public void Initialize(InitializationEngine context)
        {
            if (context.HostType == HostType.WebApplication)
            {
                var registry = context.Locate.Advanced.GetInstance<MetadataHandlerRegistry>();
                registry.RegisterMetadataHandler(typeof(ContentData), new ReadonlyBlockMetadataExtender());
            }
        }

        public void Uninitialize(InitializationEngine context) { }
    }
}