How to use the "$replace" to replace 6 lines?

[ChiNa]

Hi everyone. I was making one of my mods to a product last night, called PostBubble, which showes the post in postbit and legacy inside a Bubble or Box, and after many hours I managed to make it, but found out that my code is only replacing 1 line! I had to ask to remove my thread again, I have only learned replacing from 1 line, to replace. And the code that I have to replace, has 6 Rows / Lines!

And even I replace that 1 line, the code appears twice in my postbit

Below you see the lines that I have to replace:

<!-- message -->
        <div id="post_message_$post[postid]">
            $ad_location[ad_showthread_firstpost_start]
            $post[message]
        </div>
        <!-- / message -->

Now my point that I have a class called <div class="red"> </div>
And I am trying to wrap 6 lines with DIVs , so it looks like this:

<div class="red">
<!-- message -->
        <div id="post_message_$post[postid]">
            $ad_location[ad_showthread_firstpost_start]
            $post[message]
        </div>
        <!-- / message -->
 </div>

Below is my replace code, for postbit and postbit_legacy:

$replace = '<!-- message -->';
        $vbulletin->templatecache['postbit'] = str_replace($replace,$replace.fetch_template('MYCODEHERE'),$vbulletin->templatecache['postbit']);
        $vbulletin->templatecache['postbit_legacy'] = str_replace($replace,$replace.fetch_template('MYCODEHERE'),$vbulletin->templatecache['postbit_legacy']);

And as you see I only have the options to replace !-- message -->, and so far this is what I know! Now hopefully someone could teach me or explain how to replace all the 6 Rows / Lines or tell me another method to put the divs arround these 6 lines.

THANK YOU VERY MUCH IF YOU COULD HELP ME OUT WITH THIS!