<?php

$pages_array[]->slug = "index";
$key = array_search(end($pages_array),$pages_array );
$pages_array[$key]->title = "Site Index";  
$pages_array[$key]->template = "interior";

$pages_array[]->slug = "a";
$key = array_search(end($pages_array),$pages_array );
$pages_array[$key]->title = "100% Wide (Layout A)";
$pages_array[$key]->template = "interior";

$pages_array[]->slug = "homepage";
$key = array_search(end($pages_array),$pages_array );
$pages_array[$key]->title = "Homepage";
$pages_array[$key]->template = "homepage";

print_r($pages_array);

?>

Array
(
    [0] => stdClass Object
        (
            [slug] => index
            [title] => Site Index
            [template] => interior
        )

    [1] => stdClass Object
        (
            [slug] => a
            [title] => 100% Wide (Layout A)
            [template] => interior
        )

    [2] => stdClass Object
        (
            [slug] => homepage
            [title] => Homepage
            [template] => homepage
        )

)