Exclude function from running on a certain page

Question

I'm working on modifying the Keyboard Shortcut Navigation plugin to fit my site. Here's the plugin: http://wordpress.org/extend/plugins/easy-keyboard-shortcut-navigation/

I don't want this plugin to run on page 2020. I've tried && !is_page('2020') and || !is_page('2020') in the elseif below, but it keeps running the function.

Any ideas?

Edit update: As requested, I'm removing the snippet and including the full code from the plugin located at the above URL.

add_action('wp_footer','keyboard_shortcut_navigation');
function keyboard_shortcut_navigation(){
    global $paged, $wp_query;
    if ( !$max_page )
        $max_page = $wp_query->max_num_pages;
    if ( !$paged )
        $paged = 1;
    $nextpage = intval($paged) + 1;
?>
<?php if( is_single() ) : ?>
<script type="text/javascript">
    document.onkeydown = chang_page;function chang_page(e) {
    var e = e || event,
    keycode = e.which || e.keyCode;
    var obj = e.target || e.srcElement;
    if(obj.tagName.toLowerCase()=="textarea"){return;}
    if(obj.tagName.toLowerCase()=="input"){return;}
    if (keycode == 33 || keycode == 37) location = '<?php echo get_permalink(get_adjacent_post(false,'',false)); ?>';
    if (keycode == 34 || keycode == 39) location = '<?php echo get_permalink(get_adjacent_post(false,'',true)); ?>';
    }
</script>
<?php elseif( is_home() || is_category() ) : ?>
<script type="text/javascript">
    document.onkeydown = chang_page;function chang_page(e) {
        var e = e || event,
        keycode = e.which || e.keyCode;
        var obj = e.target || e.srcElement;
        if(obj.tagName.toLowerCase()=="textarea"){return;}
        if(obj.tagName.toLowerCase()=="input"){return;}
        if (keycode == 33 || keycode == 37) location = '<?php echo get_previous_posts_page_link(); ?>';
        if (keycode == 34 || keycode == 39) 
        <?php if ( $nextpage <= $max_page ) : ?>
            location = '<?php echo get_next_posts_page_link(); ?>';
        <?php else : ?>
            location = '<?php echo get_pagenum_link( $max_page ); ?>';  
        <?php endif; ?>
    }
</script>
<?php endif; ?>
<?php
}

Answer 1

This works for a page on my site with ID 675:

function tst($content) {
  if (is_page(675)) print('howdy');
}
add_action('wp_footer','tst');

I would just interrupt the function right at the top.

function keyboard_shortcut_navigation(){
    global $paged, $wp_query;
    if (is_page(2020)) return; // for a post with ID 2020
    if (is_page('2020')) return; // for a post with slug or title "2020"
    // you should only need one of those
    // ... the rest

If you are talking a posts instead of pages then maybe what you want is this:

// old
<?php if( is_single() ) : ?>
// new
<?php if( is_single() && !is_single(2020)) : ?>
// use quotes if 2020 is the title or the slug

You are hacking somebody else's plugin so you are likely to have problems when you update. I'd contact the author and ask for a hook in the next release that will allow you to do this without hacking anything.