Add Custom pages in the display area of entity instead of the system provided area

When you click on any entity in an area, the records of the entity are displayed in a grid in an aspx page. 

There is one thing that this aspx page is not fully customizable. But, there is an option to replace this page as such. This can be done by using the sitemap of the application.

Download the sitemap of the application. And, in hte URL attribute of the entity for which you want to display your custom aspx page. This sitemap when successfully imported into the application will display your custom page instead of the system page.