How can I create custom in-post templates?

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First of all : Cool idea.
I don’t know whether there exists a plugin for this task, but I would simply implement this as a new small plugin.

I would recommend changing your syntax, so that it won’t contain the links as html.

I changed it to:

{{previousKnowledge|first=...|second=...}}

Here is my simple first approach :

<?php
    /*
     Plugin Name: Previous Knowledge
    Plugin URI: TODO
    Description: TODO
    Author: xaeDes
    Version: 0.1
    Author URI: TODO
    License: GPL2
    */


    function previous_knowledge_preg_replace_callback( $matches ) {
        //$matches[1] contains the "https://wordpress.stackexchange.com/questions/46725/..." in '{{previousKnowledge|...}}'
        $items = explode("|", $matches[1]);
        $replaced = '<div id="previousKnowledge"><ul>';
        foreach( $items as $item ) {
            $item_info = explode("=",$item);
            $replaced .= "<li><a href="https://wordpress.stackexchange.com/questions/46725/${item_info[1]}">${item_info[0]}</a></li>";
        }
        $replaced .= '</ul></div>';
        return $replaced;
    }

    /**
     * Looks for occurrences of {{previousKnowledge|...}} tags and replaces them by html.
     * @param string $content
     * @return string
     */
    function previous_knowledge_content_filter( $content ) {
        return preg_replace_callback('#{{previousKnowledge\\s*\\|(.+)}}#i','previous_knowledge_preg_replace_callback', $content);
    }

    add_filter( 'the_content' , 'previous_knowledge_content_filter' );
?>

I tested with your example and it works.

You may change the output html in previous_knowledge_preg_replace_callback(..).

How to install it in your wordpress :

  1. Create a folder named ‘previous_knowledge’ (or whatever name you find appropriate) in wp-contents/plugins/.

  2. Create a php file named previous_knowledge.php inside this folder and paste the code into the file.

  3. Now you only have to activate it and put “{{previousKnowledge|first=…|second=…}}” into your posts or pages.

Do you want further explanations?