1. Allow [ code=Something ] tags where "Something" would become the title of the code block.
   
2. Preserve whitespace inside [ code ] tags
   
3. Don't add extra <br>s inside [ code ] tags
   
4. Don't convert tabs to spaces inside [ code ] tags
   

• Go to Admin CP -> Configuration -> MyCode (on the left sidebar).
  
• Click "Add new MyCode".
  
• Title it whatever you want (I used "Improved code tags"), and set the following:
  

\[code\=(.*?)\](?|\n(.*?)\n|\n(.*?)|(.*?)\n|(.*?))\[\/code\]

<div class="codeblock">
<div class="title">$1:</div>
<div class="body" dir="ltr"><code>$2</code></div>
</div>

• Under "Enabled" select "Yes" then click Save. You're all done with #1.
  

• Go to Admin CP -> Templates and Styles and click on your theme.
  
• At the top click "Add Stylesheet".
  
• Give it a name (I used "custom.css").
  
• Select "Globally" under "Attatched to" and click "Write my own content".
  
• Paste the following into the box:
  

.codeblock code {
     white-space: pre;
}

• Click save.
  
• Go back to your theme and make sure that your new css file has the highest order
  
• Save the stylesheet ordering. You've now finished #2.
  

• Using the FTP client of your choice, go to your main MyBB directory, then to the "inc" subfolder, and edit the file "class_parser.php".
  
• At the top of the file you'll see "<?php" and underneath that you'll see a bunch of comments (inside /* */ symbols). After the comments, and above "class PostParser" (or whatever the first bit of code is) paste the following code:
  

function my_nl2br($string){
    $string = str_replace("\n", "<br />", $string);
    if(preg_match_all('/\<code\>(.*?)\<\/code\>/', $string, $match)){
        foreach($match as $a){
            foreach($a as $b){
                $string = str_replace('<code>'.$b.'</code>', "<code>".str_replace("<br />", "\n", $b)."</code>", $string);
            }
        }
    }
return $string;
}

$message = nl2br($message);

$message = my_nl2br($message);

$code = str_replace("\t", '    ', $code);
$code = str_replace("  ", '  ', $code);

//$code = str_replace("\t", '    ', $code);
//$code = str_replace("  ", '  ', $code);