Simon Wheatley

Provides a drop-down to select different templates for posts from the post edit screen. The templates are defined similarly to page templates, and will replace single.php for the specified post. This plugin will NOT switch the templates for the different posts in a listing page, e.g. a date or category archive, it will only affect the template used for single posts (i.e. you can choose a template which is not single.php).
Post templates, as far as this plugin is concerned, are configured similarly to <a href="https://codex.wordpress.org/Pages#Creating_Your_Own_Page_Templates" rel="nofollow ugc">page templates</a> in that they have a particular style of PHP comment at the top of them. Each post template must contain the following, or similar, at the top:
<pre><code><?php
/*
Template Name Posts: Snarfer
*/
?>
</code></pre>
First note: Page templates use “Template Name:“, whereas post templates use “Template Name Posts:“.
Second note: You must have the custom post template files in your theme in the same directory/folder as your index.php template file, not in a sub-directory/sub-folder.
<h3>Developers</h3>
If you want to implement the custom post templates on a custom post type, you can use the <code>cpt_post_types</code> filter, here’s an example below of adding the custom post template selector and metabox to the “Movie” and “Actor” custom post types. This code can be added to a plugin or to the <code>functions.php</code> file in your theme.
<pre><code>/**
 * Hooks the WP cpt_post_types filter 
 *
 * @param array $post_types An array of post type names that the templates be used by
 * @return array The array of post type names that the templates be used by
 **/
function my_cpt_post_types( $post_types ) {
 $post_types[] = 'movie';
 $post_types[] = 'actor';
 return $post_types;
}
add_filter( 'cpt_post_types', 'my_cpt_post_types' );
</code></pre>

Custom Post Template

Provides a drop-down to select different templates for posts from the post edit screen. The templates replace single.php for the specified post.

Ajay Kumar

Quick Child Theme Generator is a very easy, quick and user friendly plugin to create a child theme for any theme supported by WordPress CMS. It allows you to edit or add functionality to your template without having to overwrite any of the parent theme files and it will helpful for restrict losing data on WP update time. You do not need to deal with any code and configuration to create child themes. It will reduce your <code>time</code> and <code>effort</code> to create a child theme.
This plugin is providing you a way to create basic custom templates pages, those will help you to add custom code in specific pages.

Quick Child Theme Generator

Quick Child Theme Generator is a WordPress plugin and it is helpful for creating child themes quickly.

Custom Post Template vs Quick Child Theme Generator