Simple template question

[should_be_easy]

Hey all,

Ive been having some trouble wrapping my head around exactly how to get a template into another template through the use of a variable. ill show you what I mean: (by the way if you see any glaring issues please let me know. this is my first time making a plugin)

I can define my templates no problem:

function contrib_install()
{	
	//create templates
	$template = '<b>Template!</b>';
	$insert_array = array (
		"title"	=>	"template_name",
		"template"	=>	$db->escape_string($template),
		"sid"	=>	"-1",
		"version"	=>	"1.0",
		"dateline"	=>	time()
	);
	$db->insert_query('templates', $insert_array);
}

and they show up in the global template list

I can put a variable into a preexisting template:

function contrib_activate()
{
	require_once MYBB_ROOT."/inc/adminfunctions_templates.php";
	find_replace_templatesets(
		"newthread",
		"#" . preg_quote('{$posticons}') . "#i",
		'{$variable}
                 {$posticons}'
	);
}

and that too goes off without a hitch

and i can even get the template into the variable sometimes:

$plugins->add_hook("newthread_start","function_one");

function function_one()
{
	global $templates, $variable;
	$variable = eval($templates->render('template_name'));	
}

And this goes off without a hitch, all fine and dandy.

The question I have about this is how to determine which hook to use?
For my example,  the 'newthread_start' hook worked because I was modifying something on the newthread.php page

But when i tried to modify the buttons at the bottom of a post on showthread.php:
http://pixs.ru/showimage/Untitledpn_8637...441257.png


doing the exact same code as above (except substituting newthread for showthread) did not work. why is this?
The following code is exactly what I have:

In the postbit template (i think that is the one responsible for rendering the aformentioned buttons):

...

<div class="postbit_buttons post_management_buttons float_right">
{$extra_button}

...

the variable extra_button has been added

the template has also been set up:

function contrib_install()
{	
	$template = '<a id="edit_post_40" class="postbit_edit" title="Extra Button" href="TODO"> <span>Extra Button!</span> </a>';
	$insert_array = array (
		"title"	=>	"button_template",
		"template"	=>	$db->escape_string($template),
		"sid"	=>	"-1",
		"version"	=>	"1.0",
		"dateline"	=>	time()
	);
	$db->insert_query('templates', $insert_array);
}

resulting in a very simple template.

but for some reason this code does not result in any changes, like it did before:

$plugins->add_hook("showthread_ismod", "add_button"); //used to put the approved button into the showthread template if you are a mod

function add_button()
{
	global $templates, $extra_button;
	$extra_button = eval($templates->render('button_template'));
}

Thoughts?

I appoligise for my poor english it is not my first language