This looks like a deal killer for me to move to SharePoint 2013 because the missing of design view in the new SharePoint Designer. Here is the way I do list development In SharePoint 2010:

(1)    Create and deploy a custom ui web part in Visual Studio.

(2)    Create additional New, Edit and Display list forms and set them as the default forms in SharePoint Designer.

(3)    Edit the new created forms in design view.

(4)    Locate and hide the original web part.

(5)    Insert my custom web part proper location.

Only code view is available in SharePoint Designer 2013, I do not know how to hide the default web part and insert my web part (which is deploy to the farm) in code. There are suggestions to use other edit tool to edit web pages. I am not sure

(1)    How to access these form/page in SharePoint.

(2)    How to insert SharePoint web part to the form/page.

I really appreciate if you can help me out.

Hi,

Base on the description, you created web part in Visual Studio and created forms using design view in SharePoint Designer 2010. Now you want to access  the forms and insert the web part to SharePoint 2013 page.

By default in SharePoint Designer 2013, to add new forms, we can only custom forms in code view. For more information:

How to Create Custom Forms Using SharePoint Designer 2013: http://community.bamboosolutions.com/blogs/sharepoint-2013/archive/2012/09/20/how-to-create-custom-forms-using-sharepoint-designer-2013.aspx

To insert the web part, we can follow these steps:

1. Save this .webpart file to your computer.
2. Open the site in the browser, and go to the page on which you would like to place your web part.  With the page in edit mode, click the Page tab, and the Insert tab.  Click Web Part.
3. On the left side, under the web part categories, click the Browse button under Upload a web part.  Browse to that .webpart file you saved at step1. Click Upload.
4. Click to insert a web part again, and then youll see it in the Imported Web Parts category.  Click Add to add the web part to your page.

Best Regards,

Linda Li