Sample code, Episerver initialization module to hide content types which you don't own.

HideContentTypesInitialization.cs

using System;
using EPiServer.DataAbstraction;
using EPiServer.Framework;
using EPiServer.Framework.Initialization;
using EPiServer.Logging;

namespace AlloyWithFind.Business.Initialization
{
    [InitializableModule]
    [ModuleDependency(typeof(EPiServer.Web.InitializationModule), typeof(EPiServer.Forms.InitializationModule))]
    public class HideContentTypesInitialization : IInitializableModule
    {
        private static readonly ILogger Logger = LogManager.GetLogger(typeof(HideContentTypesInitialization));

        /// <summary>
        /// Customized search block Guid.
        /// </summary>
        public static readonly Guid SearchBlockGuid = new Guid("3a263af2-79d9-4275-ad15-3c3187c89870");

        /// <summary>
        /// Episerver Forms captcha element Guid.
        /// </summary>
        public static readonly Guid CaptchaBlockGuid = new Guid("0cffa8b6-3c20-4b97-914f-75a624b19bff");

        public void Initialize(InitializationEngine context)
        {
            // get content types repository
            IContentTypeRepository ctRepo = context.Locate.ContentTypeRepository();

            HideFromEditors(ctRepo, SearchBlockGuid);
            HideFromEditors(ctRepo, CaptchaBlockGuid);
        }

        private static void HideFromEditors(IContentTypeRepository repo, Guid contentGuid)
        {
            if (repo == null)
            {
                throw new ArgumentNullException(nameof(repo));
            }

            // get content with Guid (returns null if not found)
            ContentType content = repo.Load(contentGuid);

            if (content != null)
            {
                if (content.IsAvailable)
                {
                    try
                    {
                        // make writable clone, hide and save it
                        ContentType writable = content.CreateWritableClone() as ContentType;
                        writable.IsAvailable = false;
                        repo.Save(writable);

                        Logger.Information($"Content type with guid '{contentGuid}' (name: {writable.Name}) hidden from editors.");
                    }
                    catch (Exception ex)
                    {
                        Logger.Error($"Failed to hide content type with guid '{contentGuid}' (name: {content.Name}).", ex);
                    }
                }
                else
                {
                    Logger.Information($"Content type with guid '{contentGuid}' (name: {content.Name}) is already hidden from editors.");
                }
            }
            else
            {
                Logger.Warning($"Cannot hide content type with guid '{contentGuid}' because it was not found from content type repository.");
            }
        }

        public void Uninitialize(InitializationEngine context)
        {
            //Add uninitialization logic
        }
    }
}