<%@ Register TagPrefix="main" TagName="MainControl" src="~/_controltemplates/Main/MainContro.ascx" %>
<SharePoint:RenderingTemplate id="ProjMainControl" runat="server">
    <Template>
        <main:MainControl runat="server" />
    </Template>
</SharePoint:RenderingTemplate>

  private bool ChangeMyForms(SPWeb web, SPFile homePage, string TemplateName)
        {
            using (SPLimitedWebPartManager wpm = homePage.GetLimitedWebPartManager(PersonalizationScope.Shared))
            {
                var webparts = wpm.WebParts.OfType<Wp>().ToList();

                foreach (Wp wpt in webparts)
                {
                    if (!(wpt is XsltListFormWebPart))
                    {
                        continue;
                    }

                    var wp = (XsltListFormWebPart)wpt;
                    
                    string zoneId = wp.ZoneID;
                    int zoneIndex = wp.ZoneIndex;
                    var listName = wp.ListName;
                    var listId = wp.ListId;
                    var pageType = wp.PageType;

                    wpm.DeleteWebPart(wp);

                    var lfwp = new ListFormWebPart();
                    lfwp.TemplateName = TemplateName; 
                    lfwp.ListName = listName;
                    lfwp.ListId = listId;
                    lfwp.PageType = pageType;

                    wpm.AddWebPart(lfwp, zoneId, zoneIndex);
                }
            }
            return true;
        }

                    using (SPWeb web = SPContext.Current.Site.OpenWeb(SPContext.Current.Web.ServerRelativeUrl)) // мне кажется что основная моя проблема здесь!
                    { 
                        var TaskList = web.Lists.TryGetList("Задачи"); //Tasks //Lists/Tasks/EditForm.aspx
                        if(TaskList != null) //Задачи
                        {
                            SPFile newHomePage = web.GetFile(SPUrlUtility.CombineUrl(TaskList.RootFolder.Url, "NewForm.aspx"));
                            SPFile editHomePage = web.GetFile(SPUrlUtility.CombineUrl(TaskList.RootFolder.Url, "EditForm.aspx")); // Lists/Tasks/EditForm.aspx
                            ChangeMyForms(web, editHomePage, "ProjMainControl");//EditForm
                            ChangeMyForms(web, newHomePage, "ProjMainControl");//NewForm  
                        }

  }