can i separate .edmx file and .designer.cs files

hi,

you can achive this using T4 template.

In Visual Studio, a T4 text template is a mixture of text blocks and control logic that can generate a text file. The control logic is written as fragments of program code in Visual C# or Visual Basic. The generated file can be text of any kind, such as a Web page, or a resource file, or program source code in any language.

Please refer..

http://blogs.microsoft.co.il/blogs/gilf/archive/2009/12/05/t4-templates-in-entity-framework-4.aspx

http://blogs.msdn.com/b/dsimmons/archive/2008/10/27/using-t4-templates-to-generate-ef-classes.aspx

hope this help.