Issues with modifying templatecache

[Raptor]

Hello, all.

I'm attempting to replace a string in the footer template, and I'm running into an issue.

   $z_name = 'footer'; 

    if (isset($vbulletin->templatecache[$z_name])) 
    { 
        $z_temp = $vbulletin->templatecache[$z_name]; 
        $str_search = "injected_data";
        $str_replace = "fubar_123";

        // This works:
        $z_temp = str_replace($str_search, $str_replace, $z_temp); 
        // This doesn't: 
        $vbulletin->templatecache[$z_name] = $z_temp;
    }

$z_temp is getting set - if I echo out the contents, I get the correct content (the footer template contents with the replaced string). However, setting the templatecache at the end is not working: it is not set to the contents of $z_temp, and appears to be unchanged.

Any help would be appreciated!