I\'ve just updated my Visual Studio 2017 ASP.NET MVC 5 application from Bootstrap v3 to v4. I\'m finding when I add a new edit partial view using scaffolding, it is still us
The templates used by the scaffolding engine in VS are fixed. They are located in your VS install dir (e.g. %programfiles%\Microsoft Visual Studio\2017\Community\Common7\IDE\Extensions\Microsoft\Web\Mvc\Scaffolding\Templates\MvcView).
So the Bootstrap 3 classes are fixed in the T4-files provided by MS (current standard is BS3 which is added by default currently when creating a new MVC web project). Just have a look at "Edit.cs.t4" in the dir mentioned above. You will find deprecated BS3 classes like "btn-default" (which is btn-secondary in BS4) in there.
You can create your own custom T4-templates if you like. The MS ref for this task would be: https://docs.microsoft.com/en-us/visualstudio/modeling/code-generation-and-t4-text-templates