Use T4 Template
T4 is a general-purpose templating engine you can use to generate C# code, Visual Basic code, XML, HTML, or text of any kind. The first step in using T4 is to create a template file, which is a mix of literal text, code, and processing directives. The T4 template processor will transform this file into a text file of the desired type by executing the code and processing directives inside.
The below link helps you to develop custom template for entityframework using T4 template
Hope this helps