How can I edit application.master using Sharepoint Designer?

the application.master is not exposed to SharePoint Designer by default. This is for VERY good reason. Application.master lives in the _layouts directory and this location is not displayed when editing a site using SPD. If you navigate to the _layouts directory to edit and view the application.master you’ll find that you can’t view it in design mode. This should be a hint that maybe you shouldn’t be doing it. Editing pages in this folder will likely result in corruption so DON’T do it. I know, I know….if you’re like me you’re probably opening designer to do this right now because you were told not to…….don’t say you weren’t warned.