Can we change the layout of the default page template or add a customized page template here?
Those options are features rather than “page templates”, which is a term that has specific meaning in APEX.
Only the Faceted Search, Master Detail, and Wizard features use specific page templates.
All of the other features give the developer a choice of Page Mode at Step 2 of the wizard, which will determine which page template is used according to the theme defaults: Normal (Page default template); Modal Dialog (Dialog Page default template); or Drawer (Drawer page template).
Are you asking for the ability to choose a specific page template at Step 2 (the page following that illustrated)?