SharePoint Designer 2013

You need to maintain existing classic pages and forms while moving toward supported customization. SharePoint Designer 2013 reached end of support on July 14, 2026, so reinstalling it is not a supported long-term solution. There is no single replacement for all its editing capabilities. For ordinary classic page content and web parts, use the browser’s Page > Edit controls with the required permissions. For list forms, first distinguish changing the user experience from editing the underlying ASPX files. In a modern list, Integrate > Power Apps > Customize forms supports creating, viewing, and editing items; it does not act as an ASPX source editor. Use JSON form layout configuration for simpler presentation changes, or SharePoint Framework Form Customizers for developer-built forms. Inventory each existing customization, then test its replacement on a separate list or page before migrating. Retain classic pages only where needed and plan modern equivalents.