The _layouts folder is protected by SharePoint Designer because modifying the OOTB files in this directory means that SharePoint is not supported. For more information, see here and here .
For user or third-party files in _layouts, if you try to open them directly with the URL ( http: //myserver/_layouts/KWizCom_Wikiplus/CreateNew.aspx ), you will receive Error: the files in the _layouts folder are not editable. You can open them in SharePoint Designer with UNC content and not with the URL (\\ myserver \ c $ \ Program Files \ Common Files \ Microsoft Shared \ Web Server Extensions \ 12 \ TEMPLATE \ LAYOUTS \ KWizCom_Wikiplus \ CreateNew. aspx), but for now, SharePoint Designer is no different from Visual Studio or Notepad, since you will probably only have Code View, since the URLs ~ / and the virtual directory will not be resolved.
I did not use Wiki Plus, but note that this change will not only affect all web applications and site collections on the server, but any changes you make will be destroyed if the updated version of Wiki Plus is deployed to the server.
Rich bennema
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