Drupal 7 - How to override template for page like node/%/custompage

Question

I have small question about overriding template for Specific page in Drupal like this "node/%/custompage". As we know for

node/% is : page--node.tlp.php 
node/%/edit : page--node--edit.tpl.php

How about a custom page (I created in my custom module) like this 
node/%/custompage
I tried : page--node--custompage.tpl.php

But it seem doesn't work. Thank.

Answer 1

You have to check "Drupal 7 Template (Theme Hook) Suggestions" page: https://www.drupal.org/node/1089656

Furthermore you can add your own theme hook suggestions. You could implement something like that :

   /**
    * Implementation of hook_preprocess_HOOK().
    */
    function mymodule_preprocess_page(&$variables){
      if(arg(0) == 'node' && arg(2) != 'custompage')
        $variables['theme_hook_suggestions'][] = 'page__custompage';
    }