How to modify a function (PHP) between hooks

[NolF]

Ok hi
I'm trying to write my first product, and it would be a small extension to the thank you hack... Is a very small thing and can be achieve by just changing a line in the code, but I wanted to do it by using the product system... Things is I don't exactly know exactly how

to begin with the thing I want to modify is

PHP Code:

function can_delete_all_thanks()
{
    global $vbulletin;

    ($hook = vBulletinHook::fetch_hook('post_thanks_function_can_delete_all_thanks_start')) ? eval($hook) : false;

    if ($vbulletin->userinfo['usergroupid'] == '6')
    {
        return true;
    }

    ($hook = vBulletinHook::fetch_hook('post_thanks_function_can_delete_all_thanks_end')) ? eval($hook) : false;

    return false;
} 


and it would basically be to change

PHP Code:

"if ($vbulletin->userinfo['usergroupid'] == '6')" 


into

PHP Code:

if (is_member_of($vbulletin->userinfo['usergroupid'], explode("|", $vbulletin->options['post_thanks_who_delete_all']))) 


(pS: options['post_thanks_who_delete_all'] is an option created by the modification which is used to insert the usergroups)

[See attachment for the whole modification]

I', not sure if I'm being clear enough... I just can figure out what to put in the hooks to make the thing work...

I hope someone can lend me just few mins to teach me how to do it ^^
Thank you mates